Can you measure the voltage produced in the heart using an oscilloscope or multimeter
I've used oscilloscopes on numerous occasions, to view the heart voltages.
Helps to have a differential plugin (Tek 7A22, e.g.) and certainly use a 3rd wire to the torso or leg to achieve a Ground.

Most important is R*C filtering to exclude cellphone and fluorescent light trash.
10Hertz LPF is about right.