The Medtronic Intact is a recently commercialized porcine bioprosthesis. Its function and ultrasonic characteristics have not been widely studied. The authors performed a prospective Doppler echocardiographic study of 38 patients with Intact bioprosthesis (n. 19:1, n. 21:10, n. 23:9, n. 25:14, n. 27:3, n. 29:1) implanted in the aortic position and without clinical signs of dysfunction over a period of 8 +/- 5 months after surgery. The following parameters were measured: maximum and mean velocities, maximum and mean transprosthetic pressure gradients, permeability index (PI) or the ratio of subaortic to transprosthetic velocities, and the effective prosthetic surface area (S) calculated using the continuity equation. The PI and S were calculated by two methods, the first using the ratio of maximum velocities (PI1 and S1) and the second using the ratio of the velocity-time integrals (PI2 and S2). The global results were: Vmax 2.65 +/- 0.4 m/s range 1.9 to 3.7 m/s), maximum pressure gradient 29 +/- 9 mmHg (range 15-55 mmHg), mean pressure gradient 16.8 +/- 5.6 mmHg (range 9-32 mmHg), PI1 37.8 +/- 4.5 p. 100 (range 26-48%), PI2 39.1 +/- 5.5 p. 100, S1 1.25 +/- 0.19 cm2 (range 0.96-1.7 cm2) and S2 1.29 cm2 +/- 0.17 cm2. Minimal central prosthetic valve regurgitation was observed in 2 cases (5%). No correlations were found between the size of the prosthesis and blood flow velocities, pressure gradients or permeability indices. On the other hand, a correlation was observed between S and the size of the prosthesis (r = 0.88, p less than 1.10(-6) (S1); r = 0.80, p less than 1.10(-6) (S2)).(ABSTRACT TRUNCATED AT 250 WORDS)