The beneficial effect of prophylaxis for IE was studied in 229 patients with prosthetic heart valves in whom 287 diagnostic or therapeutic interventions were performed. The prevention used was similar to that recommended by the American Heart Association. Prosthetic valve endocarditis was not observed in any of these patients. This result was compared with that of 304 patients with prosthetic heart valves, in whom without any prevention 390 similar interventions were performed during the same observation period. The incidence of prosthetic valve endocarditis occurring within 14 days after the intervention was 1.5/100 interventions (n = 6). All patients had to be reoperated. One patient died perioperatively. Two more patients developed prosthetic valve endocarditis 8 and 13 weeks, respectively, after the initial intervention. This retrospective study documents the benefit of the prophylaxis for IE used.