If your goal is to test medical equipment I would suggest the
TechPatient CARDIO ECG simulator from HE Instruments.
It produces realistic cardiac waveforms with statistical control. You can control the mean and standard deviation both on amplitude and beat-rate to test QRS and beat-rate detection and AGC.
It also includes power hum noise (50Hz/60Hz and 100Hz/120Hz) to test noise filters, baseline wander and muscle tremor.
You can connect 4mm Snap, 4mm Banana and 2mm Pin patient cables, and you can also extract a high signal from its alligator cable.
