Among 304 cases of aortic valvulopathies studied for surgical selection, the authors have found a high incidence of conduction disturbances (16% in aortic stenosis and 18,4% in aortic regurgitation). The conduction defects are mostly intraventricular among stenosis isolated or associated to regurgitation and mostly atrio-ventricular among pure aortic insufficiencies. The highest incidence (30%) being found in patients with bacterial endocarditis acute or healed. The incidence of conduction disturbances increases with age, with the presence of valvular calcifications, of left ventricular strain or failure, of coronary insufficiency and angina... practically with the duration and the severity of the valvular disease. Surgical risk is heavier and natural prognosis poorer in valvulopathies with conduction disturbances. But these disturbances never contraindicates surgery : it is sometimes necessary to insert a pacemaker with or without valvular replacement mostly in aortic stenosis with infrahisian conduction defects. During hemodynamic investigation of such cases one must be ready to stimulate the heart, particularly during right heart catheterization of patients with complete left bundle branch block.