The Edwards MIRA bileaflet mechanical prosthesis, a heart valve not yet available in the United States, is designed with a unique hinge mechanism, curved leaflets, and thin titanium housing. We performed this study to investigate its clinical performance and postoperative hemodynamic results. We implanted 58 Edwards MIRA prostheses in 51 patients in the aortic (n = 18), mitral (n = 26), and aortic and mitral (n = 7) positions. Patients' ages ranged from 25 to 84 years (mean age, 53.7 +/- 13.6). Operative mortality was 2% (n = 1), and late mortality was 4% (n = 2). Thromboembolic events were observed in 2 patients (valve thrombosis in 1 and a cerebrovascular event in 1). There were no complications related to anticoagulation. No signs of valvular dysfunction or paravalvular leakage were observed. Peak transvalvular gradients of the aortic prostheses ranged from 24.25 +/- 5.32 mmHg for the 21-mm valve to 11 +/- 1.41 mmHg for the 25-mm valve. The effective orifice area ranged from 1.99 +/- 0.12 cm2 for the 21-mm valve to 2.44 +/- 0.17 cm2 for the 25-mm valve. The mean transvalvular gradients of the mitral prostheses ranged from 5.85 +/- 2.91 mmHg for the 27-mm valve to 4.5 +/- 0 mmHg for the 31-mm valve. The effective orifice area ranged from 2.31 +/- 0.03 cm2 for the 27-mm valve to 2.64 +/- 0.05 cm2 for the 33-mm valve. These preliminary data suggest good hemodynamic function and a low rate of valve-related complications in the use of the Edwards MIRA mechanical prosthesis.