Source

File: wp-admin/includes/misc.php

function wp_refresh_heartbeat_nonces( $response ) {
	// Refresh the Rest API nonce.
	$response['rest_nonce'] = wp_create_nonce( 'wp_rest' );

	// Refresh the Heartbeat nonce.
	$response['heartbeat_nonce'] = wp_create_nonce( 'heartbeat-nonce' );
	return $response;
}