With my setup there are many problems, not in it's principle which is sound (well S4 sounds) but in practical:
It has problems detecting heart sounds with obese people, women with ample breast.
Some smart guys have a better proposal: A smart toilet seat!
The toilet seat–based cardiovascular monitoring system is completely self-contained, battery-powered, wireless, and cleanable with all sensors and electronics instrumentation integrated inside of the seat. It can measure the electrocardiogram (ECG), photoplethysmogram (PPG), and the ballistocardiogram (BCG).
I wish them a lot of success :-)