The slope of the end-systolic pressure-volume relationship (Emax), which is generated clinically by load manipulation, as well as the "absolute" peak systolic pressure end-systolic volume ratio (denoted as pressure-volume ratio), have been suggested as indices defining left ventricular function. This study represents an attempt to determine the relationship between these two indices by studying 20 patients (16 with coronary artery disease and 4 with normal coronary arteries) undergoing cardiac catheterization. Left ventriculography was performed three times in each patient: (1) in the control baseline state, (2) after rapid intravenous infusion of 250-300 cc of saline, and (3) after sublingual administration of 5 mg isosorbide dinitrate. Emax was approximated by linear regression using the peak left ventricular pressure (replacing end-systolic pressure) and the smallest left ventricular (end-systolic) volume for these three different loads. Acute ischemia with typical chest pain and ECG changes developed in 4 patients during saline loading. The pressure-volume ratio showed no change with load manipulation in patients who did not demonstrate ischemia. In the 4 patients who developed acute ischemia, the pressure-volume ratio dropped from 4.4 +/- 1.3 to 2.9 +/- 0.9 mmHg/ml (p less than 0.001). In all of the patients, the pressure-volume ratio, but not the Emax, correlated with the ejection fraction (r = 0.6; p less than 0.05). In addition, the Emax line demonstrated a markedly nonphysiological Vo. There was no correlation between Emax and pressure-volume ratio.(ABSTRACT TRUNCATED AT 250 WORDS)