Normal Rhythm:
Contraction of the heart is initiated by propagating waves of bioelectricity, shown in yellow. Under normal conditions, the heart's natural pacemaker, located in the right atrium, sends out regular electrical impulses that generate waves of electricity that propagate in a coordinated manner throughout the atria, initiating atrial contraction that pumps blood from the atria to the ventricles. The electrical impulses from the atria pass through a specialized region that delays propagation to the ventricles in order to allow time for ventricular filling. Once the electrical wave reaches the ventricles, a coordinated ventricular contraction is initiated and blood is pumped to the lungs and to the body.

If this normal electrical activity is disrupted, the result is an arrhythmia, which can affect the heart's ability to pump effectively. Click on the buttons to see simulations of four different types of arrhythmias.