I think h TS is talking about an EKG monitor that encodes the slow heartbeat waveform into a frequency modulated audio signal that is picked up by an app to display a trace

Bob.

 

That can easily be done with a VCO, and the CD4046 certainly includes a good VCO. AND the encoding can be made very precise by adding a digital divider to the feedback loop which will then produce an exact frequency multiplier.