We prospectively studied 37 consecutive patients implanted with the Carbomedics prosthetic heart value in the mitral position (without clinical evidence of prosthetic valve dysfunction) with two-dimensional and Doppler echocardiography. The peak mitral prosthetic gradient ranged from 4.60 to 14.63 (mean 8.97 +/- 2.29) mm Hg; mean mitral prosthetic gradient ranged from 1.67 to 6.18 (mean 3.24 +/- 0.95) mm Hg; pressure half-time derived mitral valve area ranged from 1.67 to 5.30 (mean 2.70 +/- 0.80) cm2. These values compare favorably with that of another bileaflet valve (i.e., the St. Jude Medical valve). There was a wide overlap in peak and mean transmitral gradients, even with the valves of the same size, with a significant but weak inverse relationship between peak mitral gradients and valve size (p = 0.03, r = -0.36). The performance index showed a smaller range of values, again with a significant but weak inverse relationship with valve size (p = 0.001, r = -0.54). The inverse relationship between valve size and peak mitral gradient and performance index should be borne in mind when analyzing Doppler hemodynamic data.