Patients with higher peak transvalvular velocities after implantation of stentless aortic bioprostheses were studied for other hemodynamic evidence of left ventricular outflow obstruction, and for change in peak velocity and evidence of left ventricular mass regression at one-year follow up. Higher early postoperative transvalvular velocity occurred more often in smaller patients, women, and with smaller valve sizes, and was associated with higher mean gradient and lower effective orifice area. In 38% of patients, higher velocities were transient. In the remaining 62%, higher velocities persisted at one-year follow up and were associated with absence of left ventricular mass regression, suggesting ‘prosthesis-patient mismatch’ and incomplete relief of left ventricular outflow obstruction.