In this study we examined the left ventricular pressure/volume relationship in 39 patients with moderate or severe aortic regurgitation (AR) and 15 normal subjects. The patients with AR were divided into two groups; patients with normal resting ejection fraction (EF ≥50%, group I, n = 21) and patients with abnormal EF (group II, n = 18). The patients in group I were younger (p < 0.005), exercised to a higher workload, and had better exercise tolerance than patients in group II (p < 0.01). The patients' exercise heart rate and blood pressure were not significantly different between the two groups. During exercise tests nine patients in group I and seven patients in group II had normal EF response (≥5% increase) (p = NS). The peak systolic blood pressure to end-systolic volume index ratio ( SBP ESVI) was higher in normal subjects than in patients in groups I and II, at rest it was (4.3 ± 1.0 vs 2.6 ± 1.2 vs 1.6 ± 0.8, respectively, p < 0.0001) and during exercise it was (7.6 ± 1.8 vs 4.2 ± 1.4 vs 2.6 ± 1.3, respectively, p < 0.0001). The resting SBP ESVI ratio was below the lower normal limit in 12 patients (57%) in group I and in 16 patients (89%) in group II. Also, the exercise SBP ESVI ratio was below the lower normal limit in 17 patients (81%) in group I and all of the patients (100%) in group II. Multivariate discriminant analysis identified the change in SBP ESVI (F = 34.8) and resting end-diastolic volume (F = 6.7) as independent predictors of the EF response to exercise. Thus, most patients with AR, including those with normal resting EF or normal EF response to exercise, have abnormal SBP ESVI at rest or during exercise. © 1985.