The sinoatrial (SA) node is the natural pacemaker of the heart. It generates electrical impulses that cause the heart’s chambers to contract, setting the heart rate. The SA node typically generates 60 ...

Sinoatrial exit block occurs when the action potential initiated by the sinoatrial node is inhibited or completely blocked before it is able to leave the SA node and reach the atrium, and thus no P ...

Junctional rhythm is an irregular heart rhythm that stems from a natural pacemaker in the heart known as the atrioventricular junction. The heart has several built-in pacemakers that help control its ...

A premature atrial contraction (PAC) occurs when a focus in the atrium (not the SA node), generates an action potential before the next scheduled SA node action potential. When this occurs prior to ...

A junctional escape rhythm is when the heartbeat starts in a different part of the heart than it should. This type of arrhythmia may not need treatment, but a doctor does need to investigate the ...

Sick sinus syndrome (SSS) is a heart rhythm problem that affects your heart's natural pacemaker. You may develop symptoms of SSS like dizziness, fainting, and fatigue. Treatment may include lifestyle ...