only 10 lines of code!

<script type="text/javascript" src="js/jquery.js"></script>
<script type="text/javascript" src=js/jheartbeat"></script>
<script type="text/javascript">
$(document).ready(function(){
$.jheartbeat.set({
   url: "data.php", // The URL that jHeartbeat will retrieve
   delay: 1500, // How often jHeartbeat should retrieve the URL
   div_id: "test_div" // Where the data will be appended.
}); });
</script>