The effects of the calcium antagonist, diltiazem (D), on left ventricular (LV) response to postextrasystolic potentiation (PESP) were investigated in 15 coronary artery disease patients. Several haemodynamic and LV function parameters, as well as regional wall kinetics, were analysed. During LV angiography, which was performed before and after D administration (0.25 mg kg-1 bolus and 1.4 microgram kg-1 min-1 infusion), programmed atrial stimulation was applied with the sequence: S1-S1 = 600 ms; S1-S2 = 400 ms; S2-S3 = 800 ms. The results indicate that D exerts a mild negative inotropic effect which is more evident in the postextrasystolic beat (postextrasystolic ESP/ESV and dP/dtmax were significantly lower after D) but the postextrasystolic increase of EF is maintained by the effects of the drug on loading conditions of the left ventricle. Our results indicate that both a reduction of afterload and an increase of preload take place after D. The greater preload reserve induced by the drug (EDVI was significantly higher in each patient after D) was associated with a slight increase in left ventricular filling rate, while end-diastolic compliance and pressure did not show significant variations. These results suggest that the increase in left ventricular preload is due to an increase in left atrial driving pressure, an improvement of left ventricular relaxation or both. D does not affect regional wall kinetics either in basal or in the postextrasystolic beat when overall areas are considered, however its effect seems to be related to the degree of basal regional contraction.(ABSTRACT TRUNCATED AT 250 WORDS)