What causes dangerous arrhythmias, like those starting in the ventricle?

The plaque in your arteries, which is crowding the passage of blood, can affect the regularity of your heartbeat. In fact, about half of all people who have coronary heart disease also end up developing electrical problems that affect the heart's rhythms (that's partly what went wrong with former Vice President Dick Cheney's heart).

The problem is instability, or you might even say, confusion. When parts of your heart muscle have died from lack of blood (because your arteries were blocked), the muscle cells that are perched on the border of those dead areas get unstable and confused, and they stop doing their job properly. They start fighting with one another, like Jerry Springer's guests, instead of supporting one another, like Oprah's. They're so busy wrangling that they stop transmitting the electrical impulses that make your heart beat.

Their fight turns into a crazy kind of dance called fibrillation. Instead of the ballet-like grace of a strong muscle moving rhythmically, you have something that looks more like a 4 a.m. dance floor-everybody moving to different beats with no regard for anything else in their way. It's deadly because none of the wiggles are strong enough to pump blood to your body. At that point, your heart may need to be shocked with a defibrillator to regain its normal rhythm, either via a paramedic or through an implanted device (such as an automatic internal cardiac defibrillator, or AICD).