Warfarin versus dipyrydamole-aspirin and pentoxifylline-aspirin for the prevention of prosthetic heart valve thromboembolism: a prospective randomized clinical trial - Mok, C K; Boey, J; Wang, R; Chan, T K; Cheung, K L; Lee, P K; Chow, J; NG, R P; Tse, T F (Circulation, 1985)