This is a simple design of a two-lead EKG amplifier. The real work is done by the AD624 inamp. In order to get rid of 60Hz, the amplifier is followed by two Sallen-Key low-pass filters. It turns out that only the first one is necessary. The second one reduces the rise and fall time of the QRS pulse.

The trickiest part of making this work is the leads.  By just holding the leads with left and right hand, there is a lot of baseline wander.  Best result is obtained using actual EKG sense pads.