There is a risk of thromboembolic complications in patients with prosthetic heart valves, to reduce this risk, anticoagulant drugs should be used. Besides thromboembolic events in pregnant women with prosthetic heart valves, anticoagulants may cause embryopathy, abortion, C.V.A. and valve thrombosis in mothers with generally high mortality. So, this study was performed to determine the pregnancy outcome in patients with prosthetic heart valves in Shahid Rajaee Heart Hospital. Eighty women aged 12-45 years old who underwent heart valve replacement at this hospital between 1978 and 1998 were included in this study. In these patients who had warfarin therapy during the whole period of pregnancy, 144 pregnancy and 18 elective abortion was occurred. Mitral Valve Replacement (MVR) was performed in 58.7%, Aortic Valve Replacement (AVR) in 16.3% and MVR plus AVR in 25%.Generally, 89.68% of the pregnancies were without any complications for mothers, but 5.56% of them had complications such as C.V.A., hypertention, edema, dyspnea and prosthetic valve malfunction. Mother death occurred in 4.76% of them. There were 38.09% normal birth with healthy baby, 50% abortion, 3.18% congenital deformities and 8.73% infant death following premature delivery, still birth and maternal death during pregnancy. Our findings showed that fetal and maternal complications in women with prosthetic heart valve using anticoagulant drugs were more common in comparison with the normal population and suggests the more clear and complete assesments in this respect. Although most pregnancy losses in women with prosthetic valve were due to warfarin use, in cases the dose of warfarin is less than 5mg/day, shifting to heparin is not recommended because a low dose of warfarin has low maternal and fetal risks.