The heartbeat starts in a specialized group of cells called the sinoatrial (SA) node, located in the upper part of the right atrium. Often referred to as the heart’s natural pacemaker, the SA node contains specialized cells that spontaneously generate electrical impulses. These electrical signals typically originate 60–100 times per minute in a healthy adult at rest, setting the normal heart rhythm known as sinus rhythm. This remarkable ability enables the heart to pump blood efficiently throughout your lifetime, beating nearly 100,000 times a day without conscious effort.
The electrical impulse follows a precise pathway: SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers. The electrical impulse generated by the SA node travels through the heart in less than one second.
Its electrical activity results from the movement of charged particles called ions across the membranes of heart cells, like Sodium, Potassium and Calcium. As these ions move in and out of cardiac cells through specialized ion channels, they create tiny electrical currents known as action potentials. These action potentials trigger muscle contraction and coordinate every heartbeat.
The heart possesses automaticity, meaning it can generate electrical impulses independently. It does not require signal from brain to contract. Although the brain influences heart rate through the autonomic nervous system.
The electrical activity of the heart is measured using an electrocardiogram (ECG). An ECG records the tiny electrical signals generated during each heartbeat and displays them as characteristic waves: like P wave, QRS complex or T wave. Doctors use ECGs to diagnose arrhythmias, heart attacks, electrolyte disturbances, conduction abnormalities, and many other cardiac conditions. Abnormalities in the heart’s electrical conduction can lead to arrhythmias, where the heart beats too fast, too slow, or irregularly. When the heart’s natural pacemaker fails or conduction pathways become blocked, doctors may implant an artificial pacemaker.
MBH/DB