Infective endocarditis still has an important morbidity and mortality in the acute phase and also in the following years. Because of this, the development and use of preventive strategies have been an important target in developed countries. Until we have some prospective studies their use will be only intuitive and based on the following criteria: endocarditis frequently follows a bacteremia; some diagnostic or therapeutic procedures cause bacteremia; the germs are habitually predictable in each procedure and are sensitive to specific antibiotics; patients with some cardiac or major structural defects have a higher risk of endocarditis. For these reasons, a rational treatment is to give the specific antibiotic against the microorganism prophylactically before it enters the bloodstream during the procedure. Although available data are inconclusive and sometimes even contradictory, most authors recommend the indication of prophylactic measures whose efficacy depends on three basic points: a) identification of patients with a high risk of endocarditis, especially those with a prosthetic cardiac valve; b) knowledge of procedures that need chemoprophylaxis, especially dental and oral procedures, and c) selection of the best prophylactic policy in each specific case. In summary, it is necessary to know to "whom", "when" and "how" to apply prophylactic measures. There are some special situations that must be considered carefully: patients treated with anticoagulant drugs or with a cardiac pacemaker or with an implanted defibrillator, patients with renal insufficiency and an arteriovenous fistulae, and some patients needing open heart surgery, or those who have already had open heart surgery. In conclusion, the prevention of bacterial endocarditis using antibiotics is currently practiced in clinical settings, especially in some specific groups of patients. It is necessary to recommend this treatment in high risk patients (i.e. in those with prosthetic cardiac valves) before a high risk procedure (i.e. dental procedures known to induce gingival or dental bleeding, including professional cleaning) and in medium risk patients, the indication must always be based on an individual analysis according to American Heart Association guidelines.