Why do some people with a heart murmur require antibiotics when they go to the dentist?

Normal heart valves have relatively "non-stick" surfaces. However, a diseased leaky or stenotic valve loses this property. In addition, turbulence of blood flow across the diseased valve allows any particles that may be present in the blood to settle on the valve and infect it. Bacteria can enter the bloodstream during infection anywhere in the body. They can also enter the bloodstream from the oral cavity, during tooth cleaning or other dental work. People with heart murmurs are felt to be at a somewhat increased risk of valve infection and should therefore take antibiotics before having dental work. The usual antibiotics used for this purpose are amoxicillin, erythromycin, and clindamycin.