OBJECTIVE Flow analysis in normally functioning eccentric monocuspid aortic prosthetic valves, to obtain a reference data list. METHODS To analyse, using 2D-Doppler Echocardiography, aortic flow velocity and systolic time intervals in clinically normal patients (pts), by physical examination. METHODS Referred pts to the Echocardiographic Laboratory at Santa Marta Hospital--HCL. METHODS Sequential sample of 61 pts with aortic prosthesis (41 Bjork-Shiley and 20 Hall-Kaster) without clinical evidence of either cardiac failure or significant aortic regurgitation. Patients with bad quality record were also excluded. METHODS Doppler Echocardiography was used to record transaortic flow, and the following indexes were analysed: instantaneous peak velocity (pv) and gradient (pg), presence of regurgitation, systolic time intervals and both preejection period/ejection time (PEP/ET) and acceleration time/ejection time (AT/ET). RESULTS Pv ranged from 1.1 to 4 m/sec (mean 2.4 +/- 0.2. The prosthesis size 19 and 21 showed a greater pg compared to the larger ones: 46.3 +/- 14.4 mmHg against 12.6 +/- 6.4 mmHg (p less than 0.001). Occasionally a pg over 50 mmHg was found in the prosthesis size 19 and 21. The correlation between prosthesis size and pg was also significant (r = -0.62; p less than 0.001). PEP interval was 60 +/- 10 milisec in prosthesis no. 19 and 90 +/- 13 milisec in no. 27 (p less than 0.01). AT ranged from 77 +/- 14 to 88 +/- 14 milisec (mean 82 +/- 13). ET was 294 +/- 5.4 milisec in valves size 19 and 257 +/- 34 millisec in no. 25 (p less than 0.05); there was also a significant difference between prosthesis size 19 and 27 (p less than 0.05). Mild regurgitation was detected in 32.7% of cases. CONCLUSIONS These data may be particularly useful as reference values to the follow-up of pts these types of prosthesis. Significant differences were found in pg between different valve sizes and this should be remembered when proceeding to standard evaluation by 2D-Doppler Echocardiography. Regurgitation is frequently detected in normally functioning prosthesis, not deeper than 2 cm in the left ventricle.