Premature ventricular contraction (PVC), also known as ventricular premature beat (VPB) or extrasystole, is a form of irregular heartbeat in which the ventricle contracts prematurely. This may be perceive as a "skipped beat" or as palpitations. The depolarization of cardiac myocytes begins in the ventricle instead of the usual place, the sinoatrial node. PVCs can be a useful natural probe, since they induce Heart rate turbulence whose characteristics can be measured, and used to evaluate cardiac function.