The purpose of this study is to:

1. Assess for hemodynamic differences at rest and with exercise between three clinically available tissue aortic valves.
2. Assess for differences in left ventricular (LV) reverse remodeling (recovery of LV hypertrophy, and changes in LV systolic and diastolic function) after aortic valve replacement for severe aortic stenosis (AS) between three clinically available aortic valve bioprosthesis.

Various aortic valve prostheses have unique hemodynamic characteristics, and there is on-going interest in defining those hemodynamic characteristics in the interest of avoiding residual LV outflow obstruction and prosthesis-patient mismatch (residual LV outflow obstruction despite a normally functioning prosthesis ) after aortic valve replacement. Attempts to compare hemodynamics between prostheses have been limited by different sizing systems used by various manufacturers (precluding meaningful comparison of valves by valve size) and biological variability of in vivo gradients and effective orifice area for any valve (making potentially small differences in hemodynamics difficult to detect). Assessment of hemodynamics during increased cardiac output associated with exercise testing has been used to better define potentially subtle differences in hemodynamics between valve prostheses. In addition, assessment for change in LV geometry (notably including LV hypertrophy) after aortic valve replacement has been used as a surrogate marker of aortic prosthesis hemodynamics.

Inclusion Criteria:

• Age ≥ 18 years.
• Severe aortic stenosis (AS) based on overall clinical impression, with or without aortic valve mean gradient ≥ 40 mm Hg, EOA < 1.0 cm2, or EOA index < 0.6 cm2/m2.
• Scheduled for clinically indicated elective aortic valve replacement for a primary diagnosis of severe AS.
• Less than moderate aortic regurgitation on preoperative testing.
• Isolated aortic valve replacement; or aortic valve replacement with concomitant coronary artery bypass grafting, ascending aorta repair, or mitral and/or tricuspid annuloplasty for functional mitral regurgitation / tricuspid regurgitation.
• Left ventricular ejection fraction ≥ 40% on preoperative testing.
• Physically able and willing to pedal a recumbent bicycle.
• Patient and surgeon agree that the patient will undergo valve replacement with a bioprosthesis.
• Patient and surgeon agree that the use of one specific bioprosthesis manufacturer / model is not indicated based on clinical criteria.
• Willing to undergo randomization to have implanted one of three bioprosthesis at the time of aortic valve replacement.
• Willing and able to undergo preoperative echocardiography/Doppler for purposes of the research study.
• Willing and able to undergo post-operative exercise stress echocardiography/Doppler 5 to 7 months after valve replacement for purposes of the research protocol.

Exclusion Criteria:

• Age < 18 years.
• AS felt by overall clinical impression to be less than severe.
• Aortic valve replacement is urgent or emergent.
• Moderate of more aortic regurgitation on preoperative testing.
• Concomitant mitral or tricuspid valve replacement.
• Left ventricular ejection fraction < 40% on preoperative testing.
• Physically unable or unwilling to pedal a recumbent bicycle.
• Planned aortic valve replacement with a mechanical prosthesis.
• Operating surgeon believes that any one of the three protocol bioprosthetic devices is contraindicated based on clinical criteria.
• Not willing to undergo randomization to have implanted one of three bioprosthesis.
• Unwilling or unable to undergo preoperative echocardiography/Doppler for purposes of the research protocol.
• Unwilling or unable to undergo post-operative exercise stress echocardiography/Doppler 5 to 7 months after valve replacement for purposes of the research protocol.