Background: ATS mechanical valve is a recently introduced pyrolytic carbon bileaflet prosthesis. This report is to evaluate the results of hemodynamic and anticoagulant therapy after ATS valve replacement. Material and Method: From May 1995 to October 1998, 53 patients received 65 ATS prosthesis; 38 Mitral(27-33 mm), 27 Aortic(19-25 mm). 2 CABGs and 5 Tricuspid annuloplasty were taken concomitantly. The follow up period was 769 patient-months(mean 16.2$pm$10.0), varied from 1 month to 39 months with 92.5% follow up rate. All patients were evaluated with Doppler echocardiography, 7-14 days after operation. Result: NYHA functional class was improved significantly, from 2.6$pm$0.8 preoperatively to 1.3$pm$0.4 postoperatively. The average value of peak and mean transvalvular pressure gradients were 25.7$pm$13.5 mmHg, 12.7$pm$8.3 mmHg in aortic position. In the mitral position, the average values of peak and mean transvalvular pressure gradient and valve area were 5.9$pm$2.5 mmHg, 3.1$pm$0.8 mmHg and 2.9$pm$0.5 $ extrm{cm}^2$, respectively. In the anticoagulant therapy, mean INR was 2.5$pm$0.6 in mitral valve replacement and 1.9$pm$0.5 in aortic valve replacement. There was no anticoagulant related complication. During that period, there were 3 hospital death(5.9%) and 1 late death(1.9%). Conclusion: The early clinical results of the ATS heart valve replacement is quite satisfactory, and low target INR reginmen is safe. And long term follow of hemodynamic characteristics is also necessary.