When you're a heartbeat away from the presidency, you can't take chances on losing a beat. That's why Vice President Dick Cheney, who has a history of heart problems, wears a state-of-the-art implantable cardioverter defibrillator device (ICD) under his skin to instantly detect and correct any abnormal heart rhythms.

Most people have heard of pacemakers that regulate slow heart rhythms, but an ICD goes a step beyond the pacemaker. An ICD also acts as a defibrillator, slowing down fast heart rhythms as well as regulating slow rhythms.

"Having an ICD is like having a paramedic living inside you," says Steven Sloan, MD, a cardiologist specializing in electrophysiology at Doylestown Hospital. And maybe it's like having a cardiologist in there with you, too.

A too-rapid or too-slow rhythm can make the heart stop pumping blood and put you at risk for unconsciousness or death within minutes unless emergency defibrillation-shocking the heart back to normal-is immediately performed.

"The ICD has a dual function as both a detection and prevention device," explains Dr. Sloan. It works like this: The tiny, battery-operated pulse generator is implanted under the skin of the chest. Connecting lead wires are inserted through the veins and positioned on different points in the heart. The cardiologist programs the ICD to treat the patient's specific rhythm problem. The leads sense an abnormal cardiac rhythm and then deliver mild to more powerful electrical shocks to normalize the rhythm. The ICD continually monitors the heartbeat for regularity and has pacing capabilities, delivering a series of signals that can cause the heart rate to return to normal when it is slightly out of rhythm.

ICDs can also be used for patients who are at risk for developing rhythm abnormalities. Until recently, ICDs were used only for patients whose medicines had failed or patients who had already experienced a cardiac arrest. Advanced ICD technology now means that patients who have been diagnosed with a weak heart muscle may be candidates for the device.

"The ICD has the potential for benefiting 2 million additional people," notes Dr. Sloan. "The ICD prolongs life and can give many patients a great peace of mind knowing that this device can keep them from fainting during activities and, even better, will protect them from sudden cardiac arrest, no matter where they are."