Introduction: This study was designed to evaluate safety and efficacy of combined low dose aspirin andwarfarin therapy following mechanical heart valve replacement.Methods: A total of 1496 patients (686 males, mean age 35 ± 8.5 years) undergoing mechanical heart valvularreplacement were randomly divided into study (warfarin plus 75-100 mg aspirin) or control (warfarin only)group. International normalized ratio (INR) and prothrombin time was maintained at 1.8-2.5 and 1.5-2.0times of the normal value, respectively. Thromboembolic events and major bleedings were registered duringfollow up.Results: Patients were followed up for 24 ^ 9 months. The average dose of warfarin in the study and controlgroup was 2.92 I 0.87 mg and 2.89i 0.79 mg, respectively (p 0.05). The overall thromboembolic events instudy group were lower than in control group (2.1％ vs. 3.6％, p = 0.044). No statistically significant differenceswere found in hemorrhage events (3.5％ vs. 3.7％, p>0.05) or mortality (03％ vs 0.4％, p ?0.05) between the twogroups.Conclusions: Following mechanical valve replacement, combined low dose aspirin and warfarin therapy wasassociated with a greater reduction in thromboembolism events than warfarin therapy alone. This combinedtreatment was not associated with an increase in the rate of major bleeding or mortality.