Among women with valvular heart disease, those with mitral stenosis carry the greatest potential for problems during pregnancy. Asymptomatic women with aortic stenosis and only mild or moderate left ventricular outflow obstruction generally tolerate pregnancy well, as do those with regurgitant lesions. In Marfan syndrome, pregnancy should not be undertaken if the aortic root dimension exceeds 4 cm. Even if the aortic root is normal, a small increased risk of dissection is present. Women with well-functioning bioprosthetic valves and normal hemodynamics may safely undertake a pregnancy, although bioprostheses deteriorate rapidly in young people.