Some patients with aortic regurgitation develop irreversible left ventricular dysfunction. The purpose of this study was to noninvasively examine left ventricular function in patients with aortic regurgitation by determining the end-systolic stress-shortening relationship using M-mode echocardiography. Ten normal volunteers and 10 patients with chronic, isolated aortic regurgitation were studied at rest and following load and inotropic alteration by cold pressor testing. The baseline ejection phase indices of ejection fraction and percent fractional shortening did not distinguish between normals and patients with aortic regurgitation (74.6% +/- 2.8% versus 67.0% +/- 4.2%, P = NS and 37.6% +/- 2.4% versus 31.6% +/- 2.7%, P = NS, respectively.) End-systolic stress was significantly greater in patients with aortic regurgitation both at rest (107.8 +/- 11.6 dynes/cm2 X 10(-3) versus 68.4 +/- 4.8 dynes/cm2 X 10(-3), P less than 0.005) and after cold pressor intervention (122.8 +/- 13.0 dynes/cm2 X 10(-3) versus 80.1 +/- 4.0 dynes/cm2 X 10(-3), P less than 0.005). Normals showed increased fractional shortening in the presence of increasing end-systolic stress. Patients with aortic regurgitation showed decreased fractional shortening during increased stress. This response suggests either left ventricular dysfunction with increasing stress or decreased myocardial contractile reserve after cold pressor inotropic stimulation. End-systolic stress-percent fractional shortening relationship may be a sensitive indicator of early left ventricular dysfunction in patients with aortic regurgitation.