The heart is a powerful muscle that pumps blood throughout the body by means of a coordinated contraction. The contraction is generated by an electrical activation, which is spread by a wave of bioelectricity that propagates in a coordinated manner throughout the heart.

During normal rhythm, the heart beats regularly, producing a single coordinated electrical wave that can be seen as a normal electrocardiogram (ECG). During arrhythmias such as ventricular tachycardia and ventricular fibrillation, this normal behavior is disrupted and the ECG records rapid rates with increased complexity.

The underlying cause of many arrhythmias is the development of a reentrant circuit of electrical activity that repetitively stimulates the heart and produces contractions at a rapid rate. During tachycardia, a single wave can rotate as a spiral wave, producing fast rates and complexity. During fibrillation, a single spiral wave can degenerate into multiple waves. Because contraction is stimulated by the pattern of electrical waves, arrhythmias can compromise the heart's ability to pump blood and sometimes may be lethal.

Animations of both simulated and experimental recordings of reentrant waves during ventricular tachycardia and ventricular fibrillation in porcine ventricles are shown (experimental images courtesy R.A. Gray).

The contracting three-dimensional heart can be rotated and zoomed/panned by using the mouse as indicated.