Heartbeat API: How to access data already enqueued?

I found the solution to my problem was to change my_data.data.my_key to my_data.my_key. For example:

$( document ).on( 'click', '#button', function() {
    var my_data = wp.heartbeat.getQueuedItem( 'my_handle' );
    alert( my_data.my_key );
});

The queued data can be easily accessed now.