Color Doppler jet analysis is widely used to characterize the degree of mitral regurgitation (MR), but the validity of this approach in patients with ischemic or functional MR has not been established. It was hypothesized that color Doppler jet area overestimates the magnitude of MR of ischemic or functional origin. The severity of isolated MR in 170 patients was measured by using Doppler/echocardiography. Group 1 (n = 58) included patients with ischemic or functional MR, and group 2 (n = 112) included those with organic MR. The regurgitant jet area and 2 methods of quantitation (quantitative Doppler and quantitative 2-dimensional echocardiography) were measured simultaneously. In group 1, color jet area was larger (10.6 +/- 5.3 vs 8.2 +/- 5.3 cm2, p = 0.004) but corresponded to a smaller regurgitant volume and regurgitant fraction by quantitative Doppler (28 +/- 14 vs 55 +/- 46 ml, p = 0.0006, and 31 +/- 12% vs 38 +/- 20%, p = 0.02, respectively) and by quantitative 2-dimensional echocardiography (22 +/- 11 vs 49 +/- 40 ml, p < 0.0001, and 27 +/- 12% vs 36 +/- 20%, p = 0.005, respectively). Enlargement of the left-sided chambers was more marked in group 1. In ischemic/functional MR, the diagnosis of severe regurgitation by color Doppler (jet area > 8 cm2) was confirmed by quantitative methods (regurgitant fraction > or = 50%) in only 6% to 11% of patients, whereas it was confirmed in 60% to 73% of patients with organic MR (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)