What is the heart's predominant pacemaker?

The sinoatrial node, located in the right atrium, spontaneously depolarizes at an intrinsic rate of 60-100 beats per minute, which is faster than any other part of the cardiac conduction system. Because it fires most rapidly, it drives the heart rate and is termed the predominant pacemaker. All other conduction system components follow the SA node's impulse under normal physiological conditions.

The left bundle branch is part of the ventricular conduction system that transmits impulses from the bundle of His to the left ventricle; it does not initiate the heartbeat.

The right bundle branch carries impulses to the right ventricle and is a downstream conductor, not a pacemaker under normal conditions.

The atrioventricular (AV) node can act as a backup pacemaker at 40-60 bpm if the SA node fails, but under normal conditions it only conducts and delays impulses from the SA node rather than initiating them.