Can you measure a PQRST wave using a multimeter or oscilloscope, it you can will two leads be enough and why are 12 leads standard tor ECG monitoring?
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.