Though it may feel like the heart has skipped a beat, a premature heartbeat occurs when the heart's regular rhythm is interrupted by an early or even extra heartbeat. If the beat arises from locations in the atria (upper chambers) it is called premature atrial contraction (PAC). If it arises from the ventricles (lower chambers), it is called premature ventricular complexes (PVC). In most cases, neither is considered serious.
Interestingly, both skipped beats and extra beats or palpitations typically have the same cause: the heart's regular rhythm is interrupted by a premature or early beat. If the premature beat arises from the atria (upper chambers), it is called a premature atrial contraction (PAC). If it arises from the ventricles (lower chambers), it is called premature ventricular contraction (PVC). In most cases, neither is considered dangerous, though exceptions exist. The reason PACs or PVCs can sometimes be felt as a skipped beat, is that the heart gets a premature signal to squeeze before it has had time to fill with blood. The resulting heart contraction does not produce blood flow to the body. A pause is felt, and the following heart beat is more forceful than usual. If the PAC or PVC is less premature, and the heart has had time to fill with blood before receiving the early signal to squeeze, an extra beat will be felt rather than a skipped beat.
Premature beats are common in healthy people of all ages. Caffeine, alcohol, stress, and fatigue may cause PACs or PVCs to occur more frequently. If the symptoms caused by premature beats are bothersome, they can be treated with medications or catheter ablation.