Continuous wave Doppler ultrasound is a noninvasive method of determining transvalvular gradients that may overestimate the gradients of prosthetic valves. It is theorized that a valve rotated or tilted in its annulus will create abnormally high velocities that calculate into derived gradients that are greater than those actually present. An in vitro apparatus was constructed to analyze the velocities and the actual and derived gradients of prosthetic valves in less than optimal orientations. Continuous flow studies of a 27 mm Omniscience prosthesis indicated good agreement between the actual and derived gradients with the valve's major orifice oriented toward the aorta's larger radius. These values increase as the valve is tilted to decrease its net opening angle. When the valve is rotated 180 degrees, the Doppler gradients tend to overestimate the actual pressure drops. These data indicate that certain valve misorientations create velocities that overestimate the transvalvular gradients.