Cardiac rhythms refer to the pattern of electrical activity that controls the heartbeat. This activity originates from the sinoatrial (SA) node, known as the heart’s natural pacemaker. It ensures the heart beats in a coordinated and efficient manner to pump blood throughout the body. Normal Cardiac Rhythm: Normal Sinus Rhythm (NSR): Heart rate 60–100 bpm; regular rhythm; P wave before every QRS complex. Common Abnormal Rhythms (Arrhythmias): 1. Sinus Bradycardia: HR 100 bpm; caused by fever, anx