Left ventricular (LV) performance may remain normal in patients with LV volume overload from aortic regurgitation, but this entity results in progressive LV dysfunction. Impairment of myocardial reserve may remain undetected by current methods of assessing ventricular performance at rest, but the stress of exercise may demonstrate a reduction of myocardial reserve. To analyze the relationship between the myocardial supply and demand for oxygen in patients with aortic regurgitation, the ratio of the diastolic pressure-time index (DPTI) over the systolic pressure-time index (SPTI) was derived from recordings of pressure tracings during cardiac catheterizations in 14 patients with aortic regurgitation, and this ratio was compared with that of 24 normal subjects. The patients with aortic regurgitation had a DPTI/SPTI that fell with exercise (0.91 +/- 0.2 to 0.55 +/- 0.2) to lower values than did the ratio in the normal subjects (1.3 +/- 0.2 to 0.8 +/- 0.1) with stress. Among the patients with aortic regurgitation, a DPTI/SPTI ratio less than 0.50 with exercise identified two groups of patients that were not well separated by more common indices of severity of aortic regurgitation. The only other parameter that separated these two groups was the end-systolic volume, which is an index that reflects myocardial contractile function independent of preload. The DPTI/SPTI ratio that falls to abnormal levels with exercise may accurately reflect a failure of myocardial reserve in aortic regurgitation.