What is the difference between PAC (Premature Atrial Contraction) and PVC (Premature Ventricular Contraction) on an ECG?

Premature Atrial Contraction (PAC) occurs when the heart's upper chambers contract too early, causing an abnormal heartbeat on an ECG. Premature Ventricular Contraction (PVC) happens when the heart's lower chambers contract prematurely, also leading to an abnormal rhythm on an ECG. The key difference is the origin of the early contraction within the heart's chambers.