PURPOSE: To establish the range of normal values by Doppler echocardiography of the parameters inherent to the hemodynamic performance of the Lillehei-Kaster (LK) and Medtronic Hall (MH) prosthetic valves (V), in the 23 mm (LKV-16, MHV-23) and 25 mm (LKV-18, MHV-25) outer diameter valves, in the aortic position. METHODS: Doppler echocardiography was performed in 32 asymptomatic patients, with normally functioning prosthetic aortic valves (8 of each type). RESULTS: The peak velocity of aortic jet was 3.13 +/- 0.46 m/sec for the LKV-16, 2.76 +/- 0.31 m/sec for the MHV-23, 2.82 +/- 0.48 m/sec for the LKV-18 and 2.43 +/- 0.36 m/sec for the MHV-25. The maximal pressure gradient was 39.84 +/- 12.05 mmHg for the LKV-16, 30.70 +/- 6.80 mmHg for the MHV-23, 32.60 +/- 10.75 mmHg for the LKV-18 and 24.11 +/- 6.70 mmHg for the MHV-25. The mean pressure gradient was 24.25 +/- 7.09 mmHg for the LKV-16, 18.50 +/- 4.41 mmHg for the MHV-23, 18.21 +/- 6.95 mmHg for the LKV-18 and 13.57 +/- 4.17 mmHg for the MHV-25. The valve effective orifice area, considering the left ventricle outflow area determined by two-dimensional echocardiography in the continuity equation, was 0.62 +/- 0.13 cm2 for the LKV-16, 1.05 +/- 0.21 cm2 for the MHV-23, 0.98 +/- 0.22 cm2 for the LKV-18 and 1.36 +/- 0.36 cm2 for the MHV-25. Considering the left ventricle outflow area equivalent to the valve sewing ring area, the valve effective orifice area was 1.40 +/- 0.23 cm2 for the LKV-16, 1.65 +/- 0.19 cm2 for the MHV-23, 1.91 +/- 0.43 cm2 for the LKV-18 and 2.37 +/- 0.56 cm2 for the MHV-25. The Doppler velocity index was 0.34 +/- 0.05 for the LKV-16, 0.40 +/- 0.04 for the MHV-23, 0.39 +/- 0.09 for the LKV-18 and 0.49 +/- 0.11 for the MHV-25. CONCLUSION: Significant hemodynamic performance superiority of the MHV over the LKV was registered, indicating that the small LKV (LKV-16 or smaller) should be avoided.