A pacemaker is a small device that helps control your heart beat by providing low-energy electrical pulses that keep the heart beating normally. Pacemakers are similar to defibrillators, but they only provide low-energy shocks and are unable to restart the heart with high-energy shocks. The device consists of two parts: it has a pulse generator that contains a battery and a small computer that regulates the rate of electrical pulses sent to your heart and leads (electrodes) with insulated wires which are placed in a chamber, or chambers of your heart and deliver the electrical impulses to adjust your heart rate. Pacemakers can have one, two, or three wires; your doctor will decide which kind of pacemaker you need based on your specific condition. Your doctor will implant the device by making a pocket in the tissue under your skin to hold the pacemaker and then threading the wires into a vein and guiding them to the right place in your heart.  There are single chamber, dual chamber and biventricular pacemakers.