Abstract: Objective To investigate the in vivo effective orifice area (EOA) and whether prosthesispatient mismatch (PPM) is going to happen after 19mm St.Jude Regent valves replacement were performed. Methods Twentythree patients with valvular heart diseases were divided into 2 groups according to aortic annular diameter. 19mm St. Jude Regent valves were replaced in aortic valve place (Regent valve group), and 21mm other doubleleaflet mechanical valves were replaced in aortic place (other valves group). All of the operations were accomplished under cardiopulmonary bypass in West China Hospital. All of the patients were followed up in 3 to 6 months after their surgery processes. Color Doppler echocardiography was used to measure the hemodynamic parameters in their followup. Then left ventricular mass (LV mass), EOA and effective orifice area index (EOAI) etc. were calculated and compared by using SPSS 12.0. Results No cardiac episodes were detected during the perioperative period and 36 months after operation. LVmass reduced in 36 months after operation in both groups. No statistical significance of EOA, EOAI and LVmass reduction were detected between the two groups. Conclusions (1)The EOA and in vivo hemodynamic effects of 19mm Regent valve are similar to 21mm other double leaflet mechanical valve. (2)It is safe to use 19mm Regent valve in those patients whose aortic annular diameter are small and need double valve replacement. Using 19mm Regent valve will not cause short time cardiac episodes and PPM. (3)More further works should be done to make sure what is the standard of PPM in Chinese people, such as enlarging the patients number and prolonging the followup time. (4) Further clinical and followup works should be done to make St.Jude Regent valve’s feature out.