The hemodynamic outcome after aortic valve replacement (AVR) with the On-X and St. Jude Medical (SJM) HP valves was evaluated comparatively in two patient groups. The groups (n = 20 each) were computer-matched for age, gender, aortic stenosis as underlying disease, body surface area, NYHA functional class, left ventricular size, mass and function, transvalvular pressure gradients and mean implanted valve size. There were no relevant differences in cross-clamp and cardiopulmonary bypass times, intensive care unit stay, in-hospital stay and postoperative NYHA class. Transvalvular flow velocities were 2.38 ± 0.3 versus 2.38 ± 0.4 m/s (p = NS) postoperatively and 2.08 ± 0.2 versus 2.22 ± 0.3 m/s (p = NS) at one year follow up for the On-X and SJM HP valves, respectively. A relatively pronounced transvalvular reflux was diagnosed for On-X valves. No significant differences were identified between the two prostheses with regard to transvalvular blood flow velocities and pressure gradients, either postoperatively or at one-year follow up.