The occurrence of pregnancy in a patient with mitral stenosis measurably increases the demands on the heat. In handling this situation a place exists for medical therapy, therapeutic abortion, and surgical intervention, depending on the individual case. The results of mitral valvuloplasty during pregnancy in 27 patients are here reported. There were 3 maternal deaths, 1 failure to improve, and 23 moderate to marked improvements. Analysis of the causes of maternal death suggested more stringent criteria for the selection of patients, especially the elimination of patients with free mitral insufficiency. There were six fetal deaths. Twenty children, including one set of twins, were born by pelvic delivery, and one was delivered by cesarean section because of breech presentation; in addition, six normal children have been born in subsequent pregnancies. The twins were born spontaneously at term to a mother who, having miscarried in four previous pregnancies, underwent a valvuloplasty in the third month of her fifth pregnancy.