Antibiotics may be used to treat a variety of bacterial infections, including heart infections such as bacterial endocarditis. Endocarditis is an infection in vulnerable areas of the endocardium, the innermost layer of the heart chambers and valves. It often affects individuals with existing valvular heart disease, congenital defects, artificial valves, or intravenous (I.V.) drug abusers.

Infections may be caused by bacteria released into the bloodstream as a result of surgical or dental procedures, I.V. drug abuse, or from infections in other parts of the body (e.g., pneumonia; urinary tract infections).

Previous guidelines advocated that individuals who were at a high risk for endocarditis take antibiotics before any dental or medical procedure. It was thought that this preventive action may help to protect patients from bacteria that could be introduced into the bloodstream.

However, in 2007, the American Heart Association issued revised guidelines suggesting that prophylactic antibiotics before medical or dental procedures were not necessary for most patients at risk for endocarditis. These new guidelines are based on several studies that have produced no conclusive evidence to show that prophylactic antibiotic use reduced the risk of bacterial endocarditis. Additionally, the extensive use of antibiotics among heart patients resulted in concerns that these patients may develop drug-resistant strains of bacteria.

As part of the revised guidelines, antibiotics may still be used before certain medical and dental procedures for the following groups:

• Patients with prosthetic heart valves
  
• Patients with a history of endocarditis
  
• Patients with certain congenital heart defects, including those who have repaired defects under certain conditions
  
• Heart transplant recipients

Patients who have mild or asymptomatic heart conditions, such as mitral valve prolapse, are no longer advised to take antibiotics before dental procedures. Additionally, patients who have suffered from rheumatic fever, or who have connective tissue disorders such as Marfan syndrome, are no longer advised to take antibiotics before dental procedures.