Stethoscope advert

A friend forwarded me this link to a brilliant Youtube advert. You might like to use it at an event or service, or just forward it to friends who might be intrigued by the message. The idea is very simple; a man finds a stethoscope in the street and realises that everything he holds it up to sings a song of what is inside. I am not going to spoil the surprise but there is an unusual quirky ending. Can you guess what is inside the man's heart?