In patients with coronary heart disease (CHD) it is important to differentiate between reversible and irreversible left ventricular (LV) asynergy. Therefore global and regional LV function was investigated in the postextrasystolic beat (PES) and after isosorbide dinitrate (ISDN). In 24 patients LV angiograms were performed before and after ISDN. The ejection fraction (EF) was determined in a sinus beat and in PES. Regional LV performance was measured by the shortening of the length axis and six short hemiaxes. In 12 patients with normal LV function at rest EF increased from .72 +/- .04 (+/- 1 SD) to .77 +/- .04 (P less than 0.05) after ISDN and rose further to .81 +/- .02 in the PES (P less than 0.05). In 12 patients with CHD and LV asynergy EF increased from .43 +/- .12 to .47 +/- .13 after ISDN (P less than 0.05) and rose further to .57 +/- .13 in the PES (P less than 0.02). After ISDN 23/39 asynergic axes improved, 15/39 axes did not change, 1/39 axis decreased its shortening by 12%. In the PES 26/39 axes improved, 6/39 axes did not change; 7/39 axes showed less shortening, presumably due to a systolic shift of blood into dyskinetic regions with LV scar. It is concluded: The PES affects viable myocardium more than does ISDN; the PES is easier to perform and permits a more precise distinction between reversible and irreversible LV dyskinesis.