Index: src/wp-admin/includes/post.php
===================================================================
--- src/wp-admin/includes/post.php	(revision 26000)
+++ src/wp-admin/includes/post.php	(working copy)
@@ -1185,7 +1185,7 @@
 	$time = $lock[0];
 	$user = isset( $lock[1] ) ? $lock[1] : get_post_meta( $post->ID, '_edit_last', true );
 
-	$time_window = apply_filters( 'wp_check_post_lock_window', 120 );
+	$time_window = apply_filters( 'wp_check_post_lock_window', 150 );
 
 	if ( $time && $time > time() - $time_window && $user != get_current_user_id() )
 		return $user;
Index: src/wp-admin/post-new.php
===================================================================
--- src/wp-admin/post-new.php	(revision 26000)
+++ src/wp-admin/post-new.php	(working copy)
@@ -48,17 +48,9 @@
 
 wp_enqueue_script( 'autosave' );
 
-if ( is_multisite() ) {
+if ( is_multisite() || count( get_users( array( 'fields' => 'ID', 'number' => 2 ) ) ) > 1 )
 	add_action( 'admin_footer', '_admin_notice_post_locked' );
-} else {
-	$check_users = get_users( array( 'fields' => 'ID', 'number' => 2 ) );
 
-	if ( count( $check_users ) > 1 )
-		add_action( 'admin_footer', '_admin_notice_post_locked' );
-
-	unset( $check_users );
-}
-
 // Show post form.
 $post = get_default_post_to_edit( $post_type, true );
 $post_ID = $post->ID;
Index: src/wp-admin/post.php
===================================================================
--- src/wp-admin/post.php	(revision 26000)
+++ src/wp-admin/post.php	(working copy)
@@ -176,17 +176,9 @@
 			wp_enqueue_script('autosave');
 	}
 
-	if ( is_multisite() ) {
+	if ( is_multisite() || count( get_users( array( 'fields' => 'ID', 'number' => 2 ) ) ) > 1 )
 		add_action( 'admin_footer', '_admin_notice_post_locked' );
-	} else {
-		$check_users = get_users( array( 'fields' => 'ID', 'number' => 2 ) );
 
-		if ( count( $check_users ) > 1 )
-			add_action( 'admin_footer', '_admin_notice_post_locked' );
-
-		unset( $check_users );
-	}
-
 	$title = $post_type_object->labels->edit_item;
 	$post = get_post($post_id, OBJECT, 'edit');
 
Index: src/wp-includes/general-template.php
===================================================================
--- src/wp-includes/general-template.php	(revision 26000)
+++ src/wp-includes/general-template.php	(working copy)
@@ -2362,8 +2362,12 @@
  * @return array $settings
  */
 function wp_heartbeat_settings( $settings ) {
+	global $pagenow;
+
 	if ( ! is_admin() )
 		$settings['ajaxurl'] = admin_url( 'admin-ajax.php', 'relative' );
+	elseif ( in_array( $pagenow, array( 'post.php', 'post-new.php', 'edit.php' ), true ) )
+		$settings['interval'] = 15;
 
 	if ( is_user_logged_in() )
 		$settings['nonce'] = wp_create_nonce( 'heartbeat-nonce' );
Index: src/wp-includes/js/heartbeat.js
===================================================================
--- src/wp-includes/js/heartbeat.js	(revision 26000)
+++ src/wp-includes/js/heartbeat.js	(working copy)
@@ -6,11 +6,11 @@
  * to use it, please follow the development closely.
  *
  * Heartbeat is a simple server polling API that sends XHR requests to
- * the server every 15 seconds and triggers events (or callbacks) upon
+ * the server every 15 - 60 seconds and triggers events (or callbacks) upon
  * receiving data. Currently these 'ticks' handle transports for post locking,
  * login-expiration warnings, and related tasks while a user is logged in.
  *
- * Available filters in ajax-actions.php:
+ * Available PHP filters (in ajax-actions.php):
  * - heartbeat_received
  * - heartbeat_send
  * - heartbeat_tick
@@ -19,76 +19,130 @@
  * - heartbeat_nopriv_tick
  * @see wp_ajax_nopriv_heartbeat(), wp_ajax_heartbeat()
  *
+ * Custom jQuery events:
+ * - heartbeat-send
+ * - heartbeat-tick
+ * - heartbeat-error
+ * - heartbeat-connection-lost
+ * - heartbeat-connection-restored
+ * - heartbeat-nonces-expired
+ *
  * @since 3.6.0
  */
 
- // Ensure the global `wp` object exists.
-window.wp = window.wp || {};
-
-(function($){
+( function( $, window, undefined ) {
 	var Heartbeat = function() {
-		var self = this,
-			running,
-			beat,
-			screenId = typeof pagenow != 'undefined' ? pagenow : '',
-			url = typeof ajaxurl != 'undefined' ? ajaxurl : '',
-			settings,
-			tick = 0,
-			queue = {},
-			interval,
-			connecting,
-			countdown = 0,
-			errorcount = 0,
-			tempInterval,
-			hasFocus = true,
-			isUserActive,
-			userActiveEvents,
-			winBlurTimeout,
-			frameBlurTimeout = -1,
-			hasConnectionError = null;
+		var $document = $(document),
+			settings = {
+				isRunning: true,
+				screenId: '',
+				url: '',
+				lastTick: 0,
+				queue: {},
+				mainInterval: 60, // Default connect interval (in seconds)
+				tempInterval: 0,
+				originalInterval: 0,
+				countdown: 0,
+				connecting: false,
+				errorcount: 0,
+				hasConnected: false,
+				hasFocus: true,
+				userActivity: 0,
+				userActiveEvents: false,
+				connectionError: false,
+				beatTimer: 0,
+				winBlurTimer: 0,
+				frameBlurTimer: 0
+			};
 
 		/**
-		 * Returns a boolean that's indicative of whether or not there is a connection error
+		 * Set local vars and events, then start
 		 *
-		 * @returns boolean
+		 * @access private
+		 *
+		 * @return void
 		 */
-		this.hasConnectionError = function() {
-			return !! hasConnectionError;
-		};
+		function initialize() {
+			if ( typeof window.pagenow != 'undefined' ) {
+				settings.screenId = window.pagenow;
+			}
 
-		if ( typeof( window.heartbeatSettings ) == 'object' ) {
-			settings = $.extend( {}, window.heartbeatSettings );
+			if ( typeof window.ajaxurl != 'undefined' ) {
+				settings.url = window.ajaxurl;
+			}
 
-			// Add private vars
-			url = settings.ajaxurl || url;
-			delete settings.ajaxurl;
-			delete settings.nonce;
+			// Pull in options passed from PHP
+			if ( typeof window.heartbeatSettings === 'object' ) {
+				var options = window.heartbeatSettings;
 
-			interval = settings.interval || 15; // default interval
-			delete settings.interval;
-			// The interval can be from 15 to 60 sec. and can be set temporarily to 5 sec.
-			if ( interval < 15 )
-				interval = 15;
-			else if ( interval > 60 )
-				interval = 60;
+				// The XHR URL can be passed as option when window.ajaxurl is not set
+				if ( ! settings.url && options.ajaxurl ) {
+					settings.url = options.ajaxurl;
+				}
 
-			interval = interval * 1000;
+				// The interval can be from 15 to 60 sec. and can be set temporarily to 5 sec.
+				if ( options.interval ) {
+					settings.mainInterval = options.interval;
 
-			// 'screenId' can be added from settings on the front-end where the JS global 'pagenow' is not set
-			screenId = screenId || settings.screenId || 'front';
-			delete settings.screenId;
+					if ( settings.mainInterval < 15 ) {
+						settings.mainInterval = 15;
+					} else if ( settings.mainInterval > 60 ) {
+						settings.mainInterval = 60;
+					}
+				}
 
-			// Add or overwrite public vars
-			$.extend( this, settings );
+				// 'screenId' can be added from settings on the front-end where the JS global 'pagenow' is not set
+				if ( ! settings.screenId ) {
+					settings.screenId = options.screenId || 'front';
+				}
+			}
+
+			// Convert to milliseconds
+			settings.mainInterval = settings.mainInterval * 1000;
+			settings.originalInterval = settings.mainInterval;
+
+			// Set focus/blur events on the window
+			$(window).on( 'blur.wp-heartbeat-focus', function() {
+				setFrameFocusEvents();
+				// We don't know why the 'blur' was fired. Either the user clicked in an iframe or outside the browser.
+				// Running blurred() after some timeout lets us cancel it if the user clicked in an iframe.
+				settings.winBlurTimer = window.setTimeout( function(){ blurred(); }, 500 );
+			}).on( 'focus.wp-heartbeat-focus', function() {
+				removeFrameFocusEvents();
+				focused();
+			}).on( 'unload.wp-heartbeat', function() {
+				// Don't connect any more
+				settings.isRunning = false;
+			});
+
+			// Check for user activity every 30 seconds.
+			window.setInterval( function(){ checkUserActive(); }, 30000 );
+
+			// Start one tick after DOM ready
+			$document.ready( function() {
+				settings.lastTick = time();
+				next();
+			});
 		}
 
-		function time(s) {
-			if ( s )
-				return parseInt( (new Date()).getTime() / 1000 );
-
+		/**
+		 * Return the current time according to the browser
+		 *
+		 * @access private
+		 *
+		 * @return int
+		 */
+		function time() {
 			return (new Date()).getTime();
 		}
 
+		/**
+		 * Check if the iframe is from the same origin
+		 *
+		 * @access private
+		 *
+		 * @return bool
+		 */
 		function isLocalFrame( frame ) {
 			var origin, src = frame.src;
 
@@ -95,20 +149,30 @@
 			if ( src && /^https?:\/\//.test( src ) ) {
 				origin = window.location.origin ? window.location.origin : window.location.protocol + '//' + window.location.host;
 
-				if ( src.indexOf( origin ) !== 0 )
+				if ( src.indexOf( origin ) !== 0 ) {
 					return false;
+				}
 			}
 
 			try {
-				if ( frame.contentWindow.document )
+				if ( frame.contentWindow.document ) {
 					return true;
+				}
 			} catch(e) {}
 
 			return false;
 		}
 
-		// Set error state and fire an event on XHR errors or timeout
-		function errorstate( error, status ) {
+		/**
+		 * Set error state and fire an event on XHR errors or timeout
+		 *
+		 * @access private
+		 *
+		 * @param string error The error type passed from the XHR
+		 * @param int status The HTTP status code passed from jqXHR (200, 404, 500, etc.)
+		 * @return void
+		 */
+		function setErrorState( error, status ) {
 			var trigger;
 
 			if ( error ) {
@@ -120,87 +184,104 @@
 						// no response for 30 sec.
 						trigger = true;
 						break;
+					case 'error':
+						if ( 503 == status && settings.hasConnected ) {
+							trigger = true;
+							break;
+						}
+						// Pass through other error statuses
 					case 'parsererror':
-					case 'error':
 					case 'empty':
 					case 'unknown':
-						errorcount++;
+						settings.errorcount++;
 
-						if ( errorcount > 2 )
+						if ( settings.errorcount > 2 && settings.hasConnected ) {
 							trigger = true;
+						}
 
 						break;
 				}
 
-				if ( 503 == status && false === hasConnectionError ) {
-					trigger = true;
-				}
-
-				if ( trigger && ! self.hasConnectionError() ) {
-					hasConnectionError = true;
+				if ( trigger && ! hasConnectionError() ) {
+					settings.connectionError = true;
 					$(document).trigger( 'heartbeat-connection-lost', [error, status] );
 				}
-			} else if ( self.hasConnectionError() ) {
-				errorcount = 0;
-				hasConnectionError = false;
-				$(document).trigger( 'heartbeat-connection-restored' );
-			} else if ( null === hasConnectionError ) {
-				hasConnectionError = false;
 			}
 		}
 
-		function connect() {
-			var send = {}, data, i, empty = true,
-			nonce = typeof window.heartbeatSettings == 'object' ? window.heartbeatSettings.nonce : '';
-			tick = time();
+		/**
+		 * Clear the error state and fire an event
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
+		function clearErrorState() {
+			// Has connected successfully
+			settings.hasConnected = true;
 
-			data = $.extend( {}, queue );
-			// Clear the data queue, anything added after this point will be send on the next tick
-			queue = {};
+			if ( hasConnectionError() ) {
+				settings.errorcount = 0;
+				settings.connectionError = false;
+				$document.trigger( 'heartbeat-connection-restored' );
+			}
+		}
 
-			$(document).trigger( 'heartbeat-send', [data] );
+		/**
+		 * Gather the data and connect to the server
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
+		function connect() {
+			var ajaxData, heartbeatData;
 
-			for ( i in data ) {
-				if ( data.hasOwnProperty( i ) ) {
-					empty = false;
-					break;
-				}
-			}
-
-			// If nothing to send (nothing is expecting a response),
-			// schedule the next tick and bail
-			if ( empty && ! self.hasConnectionError() ) {
-				connecting = false;
-				next();
+			// If the connection to the server is slower than the interval,
+			// heartbeat connects as soon as the previous connection's response is received.
+			if ( settings.connecting ) {
 				return;
 			}
 
-			send.data = data;
-			send.interval = interval / 1000;
-			send._nonce = nonce;
-			send.action = 'heartbeat';
-			send.screen_id = screenId;
-			send.has_focus = hasFocus;
+			settings.lastTick = time();
 
-			connecting = true;
-			self.xhr = $.ajax({
-				url: url,
+			heartbeatData = $.extend( {}, settings.queue );
+			// Clear the data queue, anything added after this point will be send on the next tick
+			settings.queue = {};
+
+			$document.trigger( 'heartbeat-send', [ heartbeatData ] );
+
+			ajaxData = {
+				data: heartbeatData,
+				interval: settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000,
+				_nonce: typeof window.heartbeatSettings === 'object' ? window.heartbeatSettings.nonce : '',
+				action: 'heartbeat',
+				screen_id: settings.screenId,
+				has_focus: settings.hasFocus
+			};
+
+			settings.connecting = true;
+			settings.xhr = $.ajax({
+				url: settings.url,
 				type: 'post',
 				timeout: 30000, // throw an error if not completed after 30 sec.
-				data: send,
+				data: ajaxData,
 				dataType: 'json'
+			}).always( function() {
+				settings.connecting = false;
+				next();
 			}).done( function( response, textStatus, jqXHR ) {
 				var new_interval;
 
-				if ( ! response )
-					return errorstate( 'empty' );
+				if ( ! response ) {
+					setErrorState( 'empty' );
+					return;
+				}
 
-				// Clear error state
-				if ( self.hasConnectionError() )
-					errorstate();
+				clearErrorState();
 
 				if ( response.nonces_expired ) {
-					$(document).trigger( 'heartbeat-nonces-expired' );
+					$document.trigger( 'heartbeat-nonces-expired' );
 					return;
 				}
 
@@ -210,42 +291,55 @@
 					delete response.heartbeat_interval;
 				}
 
-				self.tick( response, textStatus, jqXHR );
+				$document.trigger( 'heartbeat-tick', [response, textStatus, jqXHR] );
 
-				// do this last, can trigger the next XHR if connection time > 5 sec. and new_interval == 'fast'
-				if ( new_interval )
-					self.interval.call( self, new_interval );
-			}).always( function() {
-				connecting = false;
-				next();
+				// Do this last, can trigger the next XHR if connection time > 5 sec. and new_interval == 'fast'
+				if ( new_interval ) {
+					setInterval( new_interval );
+				}
 			}).fail( function( jqXHR, textStatus, error ) {
-				errorstate( textStatus || 'unknown', jqXHR.status );
-				self.error( jqXHR, textStatus, error );
+				setErrorState( textStatus || 'unknown', jqXHR.status );
+				$document.trigger( 'heartbeat-error', [jqXHR, textStatus, error] );
 			});
 		}
 
+		/**
+		 * Schedule the next connection
+		 *
+		 * Fires immediately if the connection time is longer than the interval.
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
 		function next() {
-			var delta = time() - tick, t = interval;
+			var delta = time() - settings.lastTick, interval = settings.mainInterval;
 
-			if ( ! running )
+			if ( ! settings.isRunning ) {
 				return;
+			}
 
-			if ( ! hasFocus ) {
-				t = 100000; // 100 sec. Post locks expire after 120 sec.
-			} else if ( countdown > 0 && tempInterval ) {
-				t = tempInterval;
-				countdown--;
+			if ( ! settings.hasFocus ) {
+				interval = 120000; // 120 sec. Post locks expire after 150 sec.
+			} else if ( settings.countdown > 0 && settings.tempInterval ) {
+				interval = settings.tempInterval;
+				settings.countdown--;
+
+				if ( settings.countdown < 1 ) {
+					settings.tempInterval = 0;
+				}
 			}
 
-			window.clearTimeout(beat);
+			window.clearTimeout( settings.beatTimer );
 
-			if ( delta < t ) {
-				beat = window.setTimeout(
+			if ( delta < interval ) {
+				settings.beatTimer = window.setTimeout(
 					function(){
-						if ( running )
+						if ( settings.isRunning ) {
 							connect();
+						}
 					},
-					t - delta
+					interval - delta
 				);
 			} else {
 				connect();
@@ -252,71 +346,113 @@
 			}
 		}
 
+		/**
+		 * Set the internal state when the browser window looses focus
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
 		function blurred() {
-			window.clearTimeout(winBlurTimeout);
-			window.clearTimeout(frameBlurTimeout);
-			winBlurTimeout = frameBlurTimeout = 0;
-
-			hasFocus = false;
+			clearFocusTimers();
+			settings.hasFocus = false;
 		}
 
+		/**
+		 * Set the internal state when the browser window is focused
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
 		function focused() {
-			window.clearTimeout(winBlurTimeout);
-			window.clearTimeout(frameBlurTimeout);
-			winBlurTimeout = frameBlurTimeout = 0;
+			clearFocusTimers();
+			settings.userActivity = time();
 
-			isUserActive = time();
-
-			if ( hasFocus )
-				return;
-
-			hasFocus = true;
-			window.clearTimeout(beat);
-
-			if ( ! connecting )
+			if ( ! settings.hasFocus ) {
+				settings.hasFocus = true;
 				next();
+			}
 		}
 
-		function setFrameEvents() {
-			$('iframe').each( function( i, frame ){
-				if ( ! isLocalFrame( frame ) )
+		/**
+		 * Add focus/blur events to all local iframes
+		 *
+		 * Used to detect when focus is moved from the main window to an iframe
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
+		function setFrameFocusEvents() {
+			$('iframe').each( function( i, frame ) {
+				if ( ! isLocalFrame( frame ) ) {
 					return;
+				}
 
-				if ( $.data( frame, 'wp-heartbeat-focus' ) )
+				if ( $.data( frame, 'wp-heartbeat-focus' ) ) {
 					return;
+				}
 
 				$.data( frame, 'wp-heartbeat-focus', 1 );
 
-				$( frame.contentWindow ).on( 'focus.wp-heartbeat-focus', function(e) {
+				$( frame.contentWindow ).on( 'focus.wp-heartbeat-focus', function() {
 					focused();
-				}).on('blur.wp-heartbeat-focus', function(e) {
-					setFrameEvents();
-					frameBlurTimeout = window.setTimeout( function(){ blurred(); }, 500 );
+				}).on('blur.wp-heartbeat-focus', function() {
+					setFrameFocusEvents();
+					// We don't know why the 'blur' was fired. Either the user clicked in the main window or outside the browser.
+					// Running blurred() after some timeout lets us cancel it if the user clicked in the main window.
+					settings.frameBlurTimer = window.setTimeout( function(){ blurred(); }, 500 );
 				});
 			});
 		}
-
-		$(window).on( 'blur.wp-heartbeat-focus', function(e) {
-			setFrameEvents();
-			winBlurTimeout = window.setTimeout( function(){ blurred(); }, 500 );
-		}).on( 'focus.wp-heartbeat-focus', function() {
+		
+		/**
+		 * Remove the focus/blur events to all local iframes
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
+		function removeFrameFocusEvents() {
 			$('iframe').each( function( i, frame ) {
-				if ( !isLocalFrame( frame ) )
+				if ( ! isLocalFrame( frame ) ) {
 					return;
+				}
 
 				$.removeData( frame, 'wp-heartbeat-focus' );
 				$( frame.contentWindow ).off( '.wp-heartbeat-focus' );
 			});
+		}
 
-			focused();
-		});
+		/**
+		 * Clear the reset timers for focus/blur events on the window and iframes
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
+		function clearFocusTimers() {
+			window.clearTimeout( settings.winBlurTimer );
+			window.clearTimeout( settings.frameBlurTimer );
+		}
 
+		/**
+		 * Runs when the user becomes active after a period of inactivity
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
 		function userIsActive() {
-			userActiveEvents = false;
-			$(document).off( '.wp-heartbeat-active' );
+			settings.isRunning = true;
+			settings.userActiveEvents = false;
+			$document.off( '.wp-heartbeat-active' );
+
 			$('iframe').each( function( i, frame ) {
-				if ( ! isLocalFrame( frame ) )
+				if ( ! isLocalFrame( frame ) ) {
 					return;
+				}
 
 				$( frame.contentWindow ).off( '.wp-heartbeat-active' );
 			});
@@ -324,97 +460,142 @@
 			focused();
 		}
 
-		// Set 'hasFocus = true' if user is active and the window is in the background.
-		// Set 'hasFocus = false' if the user has been inactive (no mouse or keyboard activity) for 5 min. even when the window has focus.
+		/**
+		 * Check for user activity
+		 *
+		 * Runs every 30 sec.
+		 * Sets 'hasFocus = true' if user is active and the window is in the background.
+		 * Set 'hasFocus = false' if the user has been inactive (no mouse or keyboard activity)
+		 * for 5 min. even when the window has focus.
+		 *
+		 * @access private
+		 *
+		 * @return void
+		 */
 		function checkUserActive() {
-			var lastActive = isUserActive ? time() - isUserActive : 0;
+			var lastActive = settings.userActivity ? time() - settings.userActivity : 0;
 
-			// Throttle down when no mouse or keyboard activity for 5 min
-			if ( lastActive > 300000 && hasFocus )
-				 blurred();
+			if ( lastActive > 300000 && settings.hasFocus ) {
+				// Throttle down when no mouse or keyboard activity for 5 min
+				blurred();
+			}
 
-			if ( ! userActiveEvents ) {
-				$(document).on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active', function(){ userIsActive(); } );
+			if ( lastActive > 900000 ) {
+				// The user has been inactive for 15 min. Stop heartbeat.
+				// (This will also release the post lock, etc.)
+				// When the user becomes active again, heartbeat will connect straight away.
+				settings.isRunning = false;
+			}
 
+			if ( ! settings.userActiveEvents ) {
+				$document.on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active', function(){ userIsActive(); } );
+
 				$('iframe').each( function( i, frame ) {
-					if ( ! isLocalFrame( frame ) )
+					if ( ! isLocalFrame( frame ) ) {
 						return;
+					}
 
 					$( frame.contentWindow ).on( 'mouseover.wp-heartbeat-active keyup.wp-heartbeat-active', function(){ userIsActive(); } );
 				});
 
-				userActiveEvents = true;
+				settings.userActiveEvents = true;
 			}
 		}
 
-		// Check for user activity every 30 seconds.
-		window.setInterval( function(){ checkUserActive(); }, 30000 );
-		$(document).ready( function() {
-			// Start one tick (15 sec) after DOM ready
-			running = true;
-			tick = time();
-			next();
-		});
+		// Public methods
 
-		this.hasFocus = function() {
-			return hasFocus;
-		};
+		/**
+		 * Whether the window (or any local iframe in it) has focus, or the user is active
+		 *
+		 * @return bool
+		 */
+		function hasFocus() {
+			return settings.hasFocus;
+		}
 
 		/**
+		 * Whether there is a connection error
+		 *
+		 * @return bool
+		 */
+		function hasConnectionError() {
+			return settings.connectionError;
+		}
+
+		/**
+		 * Connect asap regardless of 'hasFocus'
+		 *
+		 * Will not open two concurrent connections. If a connection is in progress,
+		 * will connect again immediately after the current connection completes.
+		 *
+		 * @return void
+		 */
+		function connectNow() {
+			settings.lastTick = 0;
+			next();
+		}
+
+		/**
 		 * Get/Set the interval
 		 *
-		 * When setting to 'fast', the interval is 5 sec. for the next 30 ticks (for 2 min and 30 sec).
+		 * When setting to 'fast' or 5, by default interval is 5 sec. for the next 30 ticks (for 2 min and 30 sec).
+		 * In this case the number of 'ticks' can be passed as second argument.
 		 * If the window doesn't have focus, the interval slows down to 2 min.
 		 *
-		 * @param string speed Interval speed: 'fast' (5sec), 'standard' (15sec) default, 'slow' (60sec)
-		 * @param string ticks Used with speed = 'fast', how many ticks before the speed reverts back
+		 * @param mixed speed Interval: 'fast' or 5, 15, 30, 60
+		 * @param string ticks Used with speed = 'fast' or 5, how many ticks before the interval reverts back
 		 * @return int Current interval in seconds
 		 */
-		this.interval = function( speed, ticks ) {
-			var reset, seconds;
-			ticks = parseInt( ticks, 10 ) || 30;
-			ticks = ticks < 1 || ticks > 30 ? 30 : ticks;
+		function setInterval( speed, ticks ) {
+			var interval, oldInerval = settings.tempInterval ? settings.tempInterval : settings.mainInterval;
 
 			if ( speed ) {
 				switch ( speed ) {
 					case 'fast':
-						seconds = 5;
-						countdown = ticks;
+					case 5:
+						interval = 5000;
 						break;
-					case 'slow':
-						seconds = 60;
-						countdown = 0;
+					case 15:
+						interval = 15000;
 						break;
+					case 30:
+						interval = 30000;
+						break;
+					case 60:
+						interval = 60000;
+						break;
 					case 'long-polling':
 						// Allow long polling, (experimental)
-						interval = 0;
+						settings.mainInterval = 0;
 						return 0;
 						break;
 					default:
-						seconds = 15;
-						countdown = 0;
+						interval = settings.originalInterval;
 				}
 
-				// Reset when the new interval value is lower than the current one
-				reset = seconds * 1000 < interval;
+				if ( 5000 === interval ) {
+					ticks = parseInt( ticks, 10 ) || 30;
+					ticks = ticks < 1 || ticks > 30 ? 30 : ticks;
 
-				if ( countdown > 0 ) {
-					tempInterval = seconds * 1000;
+					settings.countdown = ticks;
+					settings.tempInterval = interval;
 				} else {
-					interval = seconds * 1000;
-					tempInterval = 0;
+					settings.countdown = 0;
+					settings.tempInterval = 0;
+					settings.mainInterval = interval;
 				}
 
-				if ( reset )
+				// Change the next connection time if new interval has been set.
+				// Will connect immediately if the time since the last connection
+				// is greater than the new interval.
+				if ( interval !== oldInerval ) {
 					next();
+				}
 			}
 
-			if ( ! hasFocus )
-				return 120;
+			return settings.tempInterval ? settings.tempInterval / 1000 : settings.mainInterval / 1000;
+		}
 
-			return tempInterval ? tempInterval / 1000 : interval / 1000;
-		};
-
 		/**
 		 * Enqueue data to send with the next XHR
 		 *
@@ -431,16 +612,17 @@
 		 * $param bool dont_overwrite Whether to overwrite existing data in the queue.
 		 * $return bool Whether the data was queued or not.
 		 */
-		this.enqueue = function( handle, data, dont_overwrite ) {
+		function enqueue( handle, data, dont_overwrite ) {
 			if ( handle ) {
-				if ( dont_overwrite && this.isQueued( handle ) )
+				if ( dont_overwrite && this.isQueued( handle ) ) {
 					return false;
+				}
 
-				queue[handle] = data;
+				settings.queue[handle] = data;
 				return true;
 			}
 			return false;
-		};
+		}
 
 		/**
 		 * Check if data with a particular handle is queued
@@ -448,10 +630,11 @@
 		 * $param string handle The handle for the data
 		 * $return bool Whether some data is queued with this handle
 		 */
-		this.isQueued = function( handle ) {
-			if ( handle )
-				return queue.hasOwnProperty( handle );
-		};
+		function isQueued( handle ) {
+			if ( handle ) {
+				return settings.queue.hasOwnProperty( handle );
+			}
+		}
 
 		/**
 		 * Remove data with a particular handle from the queue
@@ -459,10 +642,11 @@
 		 * $param string handle The handle for the data
 		 * $return void
 		 */
-		this.dequeue = function( handle ) {
-			if ( handle )
-				delete queue[handle];
-		};
+		function dequeue( handle ) {
+			if ( handle ) {
+				delete settings.queue[handle];
+			}
+		}
 
 		/**
 		 * Get data that was enqueued with a particular handle
@@ -470,21 +654,29 @@
 		 * $param string handle The handle for the data
 		 * $return mixed The data or undefined
 		 */
-		this.getQueuedItem = function( handle ) {
-			if ( handle )
+		function getQueuedItem( handle ) {
+			if ( handle ) {
 				return this.isQueued( handle ) ? queue[handle] : undefined;
+			}
+		}
+
+		initialize();
+
+		// Expose public methods
+		return {
+			hasFocus: hasFocus,
+			connectNow: connectNow,
+			setInterval: setInterval,
+			hasConnectionError: hasConnectionError,
+			enqueue: enqueue,
+			dequeue: dequeue,
+			isQueued: isQueued,
+			getQueuedItem: getQueuedItem
 		};
 	};
 
-	$.extend( Heartbeat.prototype, {
-		tick: function( data, textStatus, jqXHR ) {
-			$(document).trigger( 'heartbeat-tick', [data, textStatus, jqXHR] );
-		},
-		error: function( jqXHR, textStatus, error ) {
-			$(document).trigger( 'heartbeat-error', [jqXHR, textStatus, error] );
-		}
-	});
+	// Ensure the global `wp` object exists.
+	window.wp = window.wp || {};
+	window.wp.heartbeat = new Heartbeat();
 
-	wp.heartbeat = new Heartbeat();
-
-}(jQuery));
+}( jQuery, window ));