Based on your posting I think this is all you want :

1. Sense the heartbeat.
2. Must be as inobtrusive as possible since it has to be worn 24Hrs / day.
3. Record the count with a day/time stamp.
4. The "patient" has a healthy heartbeat.( In other words he has no problem with his heart )

If so, can one not settle for the pulse-oxymeter probes - these are clamped on to either the finger tips or ear lobes. And use the output for the counting...

But Jose, I am just thinking aloud - maybe it will help; maybe not.

Raghu