We experienced aortic valve replacement for 18 patients (4 male and 14 female, ranging from 40 to 81 years old, mean 64 years old) with small aortic annulus with new small prosthesis. Medtronic Hall 20 A (MH 20 A). The average body surface area was 1.47 m2 (range 1.28 to 1.81 m2). One patient was died of lung cancer at 3 months postoperatively. One nonstructural dysfunction and one low cardiac output syndrome was noted during operation. Sixteen survivors with MH 20 A, showed satisfactory clinical results, except for minor thromboembolism, in 2 patients. The MH 20 A had the same function as that of MH 21 A, already reported. We concluded that aortic valve replacement by Medtronic Hall 20 A prosthesis was usefull for the patient with small aortic annulus.