Arrhythmias Heart arrhythmias occur when the electrical impulses that coordinate the heartbeat don't function properly. For example, a scar from a heart attack may cause the electrical impulse to short circuit around it and veer from the normal electrical pathway. Arrhythmias may cause the heart to beat too quickly, too slowly, or irregularly.

Valve disease People can have congenital heart valve disease (that is, they were born with it), or they can acquire it later in life. Congenital valve disease usually involves pulmonary or aortic valves that didn't form properly in the womb. Acquired heart valve disease usually involves the aortic or mitral valves, which, although normal at first, become defective or diseased over time. Some acquired or congenital conditions will remain asymptomatic throughout a person's lifetime. Others, though, may worsen, and if left untreated, can cause heart failure, blood clots, or even sudden death.