The effects of i.v. administered isosorbide dinitrate (ISDN) on the reduced level of regional myocardial function during coronary occlusion were studied in conscious dogs before and after collateral development and in the absence of persistent coronary stenosis. The animals were instrumented during sterile surgery with a miniature pressure gauge for measuring left ventricular pressure and a cannula for aortic pressure. Two pairs of piezoelectric crystals were placed in normal and ischemic areas to determine regional circumferential length. A hydraulic cuff occluder and a Doppler flow probe were placed around the left circumflex coronary artery. Collaterals were induced to develop by 2 min of coronary occlusion applied repetitively at an interval of 32 min for 2 to 9 days, until the regional dysfunction produced by coronary occlusion had disappeared. Collateral development was estimated according to percentage of systolic shortening and endsystolic length area (ESL area) during the occlusion. Before collateral development, ISDN in a dose of 100 micrograms/kg did not affect the level of regional dysfunction. The ESL area was 250 +/- 54 and 248 +/- 52 mm.sec before and after ISDN, respectively. After collateral development, the ESL area was 51 +/- 13 mm.sec and it decreased by 35% after the i.v. administration of ISDN. The improvement by ISDN of transient myocardial dysfunction was achieved even during electrical tachypacing. Accordingly, the beneficial effects of ISDN on regional wall motion rendered ischemic during transient coronary occlusion were appreciable after coronary collateral development.