After Record Updated - Email with only CHANGED Fields

Hello, I would like to generate an email after any edit that contains only data fields that have changed since the last edit. I have the "Send Email with New Data" code running but that sends all the fields. How can I code the logic of comparing the old field values with the new field values within that event loop? Here is my current code:
foreach($values as $field=>$value)

$msg.= $field." : ".$value."
"."\r

";
Can anyone help with that comparison?