A CRT device sends small, undetectable electrical impulses to both lower chambers of the heart to help them beat together in a more synchronized pattern. This improves the heart’s ability to pump blood and oxygen to the body.

The heart device itself is actually a tiny computer, plus a battery, contained in a small titanium metal case that is about the size of a pocket watch. It weighs about 3 ounces.
In addition to the heart device, insulated wires called leads are implanted for two purposes: to carry information signals from your heart to the heart device, and to carry electrical impulses to your heart.

The CRT devices that have a defibrillator are typically referred to as a Cardiac Resynchronization Therapy Defibrillator or CRT-D. The CRT portion of the device coordinates the beating of the left and right ventricles so that they work together more effectively to pump blood throughout the body. However, when it senses a dangerous abnormal heart rhythm (arrhythmias), it will attempt to shock the heart back into a normal rhythm.