Figure 27-19 Summary of the normal acoustic characteristics of valve prostheses according to type and location. A₂ , aortic second sound; AC, aortic valve closure sound; AO, aortic valve opening sound; DM, diastolic murmur; MC, mitral valve closure sound; MO, mitral valve opening sound; P₂ , pulmonary second sound; S₁ , first heart sound; S₂ , second heart sound; SEM, systolic ejection murmur. (Redrawn from Smith ND, Raizada V, Abrams J: Auscultation of the normally functioning prosthetic valve. Ann Intern Med 95:594, 1981.)