In my sound effects research of the old radio days, I understand that to create heartbeats, they placed the arm of a record player on a towel or other kind of soft fabric – with the needle actually touching the cloth. Light taps on the fabric translated as low-end thumps when amplified through the record player. The “heartbeats” could then be performed as needed. I don’t know how “good” they sounded, but it’s certainly one method.
– Steve Lee

A buddy of mine created a very nice heartbeat using a large plastic trash can. The plastic popping in and out was very controllable and created two distinct in/out “pumping” sounds.
– Bob Kessler

Take a piece of fabric and hold it with a loose grip. Then quickly stretch the fabric for a pounding, heart-like sound.
– David Filskov

Bare your chest (!), position a microphone pointing at your shoulder region and then make a quick inward pull with your arms and hands and stop abruptly. Keeps you warm as well :)
– David Filskov

Any kind of thump run through a lowpass filter sequenced in a reasonably rhythmic sequence will give you the effect. It might be fun to throw in some “flushing blood” kind of liquid.
– Jamey Scott

Anyone try contact mics on a pulse point? This might work well if you also employ a BP cuff (don’t try it on the one in your neck :)
– David Steinwedel

I double the heartbeat with a kick drum. Filter anything below 60Hz, add an insane amount of mid frequency.
– Jerome Boiteau