It was the purpose of the present study to prove the feasibility and reliability of quantitative stress-echocardiography as an alternative method to radionuclide angiography (RNA) in chronic regurgitant valvular lesions. Echocardiography and RNA are most commonly used to obtain various left ventricular (LV) morphometric and functional parameters that have been postulated to predict long-term prognosis in patients with aortic and mitral valvular regurgitation. Supine bicycle ergometry with a workload ranging from 25-250 Watts was used to evaluate stress dependent LV volumes and ejection fractions (EFs) in patients with pure aortic (n = 18) and mitral regurgitation (n = 14). Most patients (23/32) underwent simultaneous right heart catheterization. Echocardiographic EFs were validated by RNA with good correlations (r = 0.81, P < 0.01). Patients with aortic regurgitation and functional class I/II (9), had a significant increase in EF during exercise (60%-67%, P < 0.001) and a reduction in end-systolic volume (71-52 mL, P < 0.01). In comparison, patients with class III symptoms (9), had a drop in EF (53%-49%, P < 0.01), had larger baseline end-systolic volume (104 mL, P = NS), which did not decrease during stress (104 vs 107 mL, P = NS). In patients with chronic mitral regurgitation baseline and exercise EF did not differ between class I/II (6) and class III (8), however, mildly symptomatic patients increased from 57%-67%, (P < 0.01) versus patients in class III (65% vs 69%, P = NS). Stroke volume index was not different at baseline (44 vs 33 mL/m(2), P = NS); however, there were significant differences during exercise (70 vs 41 mL/m(2), P = 0.05). Quantitative stress-echocardiography is a noninvasive and safe alternative method to RNA, which allows reliable calculation of stress dependent LV volumes and EF. Determination of end-systolic volumes may be of additional prognostic value. The combination of a high baseline EF and low stroke volume index with the inability to improve during exercise might reflect early stages of impaired LV function in patients with severe mitral regurgitation.