One-year echocardiography demonstrated small hemodynamic differences between Epic , Magna , and Mitroflow bioprostheses in mean gradient ( 15.2 5.5 , 12.3 4.3 , and 16.2 5.7 mm Hg , respectively ; P < .001 ) and indexed aortic valve area ( 0.93 0.28 , 1.04 0.28 , and 0.96 -0.26 cm ( 2 ) / m ( 2 ) , respectively ; P = .015 ) .