A pacemaker for heart failure, used for cardiac resynchronization therapy (CRT), sends electrical pulses to the heart to keep the lower chambers (the ventricles) pumping together. This type of pacemaker is also called a biventricular pacemaker.

A doctor places the pacemaker in the chest. The pacemaker has three wires, or leads, that connect to the heart through the subclavian vein. One lead is in the right atrium (upper chamber). A second lead is in the right ventricle. The third lead is in a vein on the outside of the left ventricle. This vein is called the coronary sinus branch vessel.