In fifteen patients with coronary artery disease who underwent hemodynamic studies, pressure measurements and left ventricular angiography were performed prior and 5' after the administration of 0.4 mg of spray nitroglycerin (TNG). Two different expressions of left ventricular diastolic compliance (dV/dP - V at end-diastole, delta V/delta P normalized by end-systolic volume-VTS) were assessed in basal conditions and after TNG. Nitroglycerin decreased left ventricular end-diastolic pressure (control 22.7 +/- 7.6 mmHg; TNG 11.4 +/- 6.1 mmHg, p less than 0.001) left ventricular end-diastolic volume (control 138 +/- 54 ml/m2, TNG 122 +/- 54 ml/m2, p less than 0.001) and improved compliance indexes (dV/dP - VED control 1.3 +/- 0.5 10(-2)/mmHg; TNG 4.6 +/- 4.3 10(-2)/MMHg; p less than 0.01; delta V/delta P - VTS control 0.071 +/- 0.04 mmHg-1; TNG 0.170 +/- 0.14 mmHg-1, p less than 0.01). TNG decreased the average value of modulus of chamber stiffness K (control 0.031 +/- 0.009; TNG 0.028 +/- 0.008, p less than 0.02) shifting the pressure-volume curve in some patients rightward and downward. Thus the increase of end-diastolic compliance (dV/dP - VED) is due to preload reduction and in patients who presented a marked decrease in K, also to the shift of the pressure-volume relation. These effects of TNG have important implications because they permit patients with coronary artery disease to engage in a given effort at a significantly lower end-diastolic pressure, avoiding pulmonary congestion.