Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
The Mysterious Human Heart The Mysterious Human Heart border=
A Series by David Grubin


Anatomy of a Pacemaker
ECG DiagramEach event on an ECG has a name. The distance between the Q and T waves can be used to diagnose hereditary diseases.
Electrical Impulses Within the Heart

Every time your heart beats, an electrical impulse generated by the sinoatrial node travels through it. The sinoatrial node is a small mass of specialized cells in the top of the right atrium that serves as the heart's natural pacemaker. The electrical activity generated there contracts the cardiac muscle, pumping blood throughout the body.

An electrocardiogram (ECG or EKG) measures the electrical activity of the heartbeat. This activity is recorded and displayed on a monitor, allowing a doctor to measure the amount of time that it takes for an electrical impulse to travel from one part of the heart to another.

In an arrhythmia, the heart's electrical activity becomes uncoordinated, and an ECG may look like a disorganized jumble of spikes and valleys. A doctor can use the ECG to determine the type of arrhythmia a patient has -- and how to treat it.

The left and right atria make the first wave seen on an ECG, called a P wave. In a normal heartbeat, the P wave looks like a short hump on the ECG. The next wave, the tall spike known as the QRS complex, indicates activity from the right and left ventricles. The final wave, or T wave, appears shorter and represents the ventricles' return to a resting state.

The amount of time that passes from the beginning of the QRS complex to the end of the T wave is referred to as the QT interval. If the QT interval is abnormally long or short, it may be due to long Q-T syndrome or short Q-T syndrome, hereditary diseases that may result in potentially fatal arrhythmias.


Funding is provided by Medtronic, AstraZeneca, and Mars, Incorporated - makers of CocoaVia. Additional funding is provided by the Fannie E. Rippel Foundation. A co-production of David Grubin Productions, Thirteen/WNET New York and WETA Washington, D.C.
Medtronic AsrtaZeneca MARS Thirteen/WNET NEW YORK