Algodoo

This doesn't really simulate a true or accurate E.C.G. waveform of a human heart, but it does generate variable rythmic waveforms that can sort of resemble an E.C.G. waveform if you adjust the frequencies of the large and small offset weights just right. Actually, the waveforms look more like a heart that is in Ventricular Fibrillation (in other words, a person who is close to death)! Use arrow keys as shown in the scene to adjust the waveform to your liking.