diff --git a/src/js/_enqueues/wp/heartbeat.js b/src/js/_enqueues/wp/heartbeat.js
index 65635177d9f66..a286a9ecee826 100644
--- a/src/js/_enqueues/wp/heartbeat.js
+++ b/src/js/_enqueues/wp/heartbeat.js
@@ -100,7 +100,12 @@
 
 				// Timer that keeps track of how long needs to be waited before connecting to
 				// the server again.
-				beatTimer: 0
+				beatTimer: 0,
+
+				// Post lock window in milliseconds. Synced from PHP via heartbeat_settings.
+				// Used to calculate the background tab heartbeat interval.
+				// Default matches the wp_check_post_lock_window default of 150 seconds.
+				postLockWindow: 150000
 			};
 
 		/**
@@ -112,7 +117,7 @@
 		 * @return {void}
 		 */
 		function initialize() {
-			var options, hidden, visibilityState, visibilitychange;
+			var options, hidden, visibilityState, visibilitychange, postLockWindow;
 
 			if ( typeof window.pagenow === 'string' ) {
 				settings.screenId = window.pagenow;
@@ -172,6 +177,14 @@
 				if ( options.suspension === 'disable' ) {
 					settings.suspendEnabled = false;
 				}
+
+				if ( options.post_lock_window ) {
+					postLockWindow = parseInt( options.post_lock_window, 10 );
+
+					if ( postLockWindow > 0 ) {
+						settings.postLockWindow = postLockWindow * 1000;
+					}
+				}
 			}
 
 			// Convert to milliseconds.
@@ -509,7 +522,11 @@
 			}
 
 			if ( ! settings.hasFocus ) {
-				interval = 120000; // 120 seconds. Post locks expire after 150 seconds.
+				// Fire 30 seconds before the post lock window expires so backgrounded
+				// tabs always refresh the lock in time. For the default 150s window this
+				// equals 120s, preserving existing behaviour. Floored at 5s for very
+				// short custom windows.
+				interval = Math.max( 5000, settings.postLockWindow - 30000 );
 			} else if ( settings.countdown > 0 && settings.tempInterval ) {
 				interval = settings.tempInterval;
 				settings.countdown--;
diff --git a/src/wp-admin/includes/misc.php b/src/wp-admin/includes/misc.php
index f021aedb8a5fb..cd8a076b0e5ab 100644
--- a/src/wp-admin/includes/misc.php
+++ b/src/wp-admin/includes/misc.php
@@ -1325,7 +1325,7 @@ function wp_refresh_heartbeat_nonces( $response ) {
 }
 
 /**
- * Disables suspension of Heartbeat on the Add/Edit Post screens.
+ * Disables suspension of Heartbeat and sets post lock data on the Add/Edit Post screens.
  *
  * @since 3.8.0
  *
@@ -1339,6 +1339,9 @@ function wp_heartbeat_set_suspension( $settings ) {
 
 	if ( 'post.php' === $pagenow || 'post-new.php' === $pagenow ) {
 		$settings['suspension'] = 'disable';
+
+		/** This filter is documented in wp-admin/includes/ajax-actions.php */
+		$settings['post_lock_window'] = apply_filters( 'wp_check_post_lock_window', 150 );
 	}
 
 	return $settings;
diff --git a/tests/phpunit/tests/admin/includes/misc/WpHeartbeatSetSuspension_Test.php b/tests/phpunit/tests/admin/includes/misc/WpHeartbeatSetSuspension_Test.php
index e799efda53353..739991f8a8fe5 100644
--- a/tests/phpunit/tests/admin/includes/misc/WpHeartbeatSetSuspension_Test.php
+++ b/tests/phpunit/tests/admin/includes/misc/WpHeartbeatSetSuspension_Test.php
@@ -79,4 +79,89 @@ public function data_wp_heartbeat_set_suspension(): array {
 			),
 		);
 	}
+
+	/**
+	 * Tests that wp_heartbeat_set_suspension() exposes the default post lock window on post screens.
+	 *
+	 * @dataProvider data_post_screens
+	 *
+	 * @ticket 65171
+	 *
+	 * @param string $pagenow_value The value for the $pagenow global.
+	 */
+	public function test_wp_heartbeat_set_suspension_sets_post_lock_window_on_post_screens( $pagenow_value ) {
+		global $pagenow;
+
+		$pagenow = $pagenow_value;
+
+		$result = wp_heartbeat_set_suspension( array() );
+
+		$this->assertArrayHasKey( 'post_lock_window', $result, "'post_lock_window' should be present when \$pagenow is {$pagenow_value}." );
+		$this->assertSame( 150, $result['post_lock_window'], "'post_lock_window' should default to 150 when \$pagenow is {$pagenow_value}." );
+	}
+
+	/**
+	 * Tests that wp_heartbeat_set_suspension() does not expose a post lock window on non-post screens.
+	 *
+	 * @dataProvider data_non_post_screens
+	 *
+	 * @ticket 65171
+	 *
+	 * @param string $pagenow_value The value for the $pagenow global.
+	 */
+	public function test_wp_heartbeat_set_suspension_does_not_set_post_lock_window_on_other_screens( $pagenow_value ) {
+		global $pagenow;
+
+		$pagenow = $pagenow_value;
+
+		$result = wp_heartbeat_set_suspension( array() );
+
+		$this->assertArrayNotHasKey( 'post_lock_window', $result, "'post_lock_window' should not be set when \$pagenow is {$pagenow_value}." );
+	}
+
+	/**
+	 * Tests that wp_heartbeat_set_suspension() honors the wp_check_post_lock_window filter.
+	 *
+	 * @ticket 65171
+	 */
+	public function test_wp_heartbeat_set_suspension_post_lock_window_respects_filter() {
+		global $pagenow;
+
+		$pagenow = 'post.php';
+
+		add_filter(
+			'wp_check_post_lock_window',
+			static function () {
+				return 60;
+			}
+		);
+
+		$result = wp_heartbeat_set_suspension( array() );
+
+		$this->assertSame( 60, $result['post_lock_window'], "'post_lock_window' should reflect the wp_check_post_lock_window filter value." );
+	}
+
+	/**
+	 * Data provider: $pagenow values for the Add/Edit Post screens.
+	 *
+	 * @return array<string, array{pagenow_value: string}>
+	 */
+	public function data_post_screens(): array {
+		return array(
+			'post.php'     => array( 'pagenow_value' => 'post.php' ),
+			'post-new.php' => array( 'pagenow_value' => 'post-new.php' ),
+		);
+	}
+
+	/**
+	 * Data provider: $pagenow values for screens that are not Add/Edit Post.
+	 *
+	 * @return array<string, array{pagenow_value: string}>
+	 */
+	public function data_non_post_screens(): array {
+		return array(
+			'index.php' => array( 'pagenow_value' => 'index.php' ),
+			'edit.php'  => array( 'pagenow_value' => 'edit.php' ),
+		);
+	}
 }