Forty-four patients with acute transmural myocardial infarction underwent cardiac catheterization 4.7 +/- 1.3 hours (+/- SD) after the onset of persistent chest discomfort. Thirty-nine patients had total occlusion of infarct-related vessels; 27 of these 39 had successful intracoronary thrombolysis. Twenty of these 27 patients (74%) had reperfusion arrhythmia. Accelerated idioventricular rhythm was most often observed with reperfusion of all myocardial zones, while sinus bradycardia and hypotension accompanied reperfusion of the inferoposterior left ventricle. Three patients with spontaneous accelerated idioventricular rhythm had patient, stenosed, infarct-related vessels on the initial coronary angiogram. Patients with unsuccessful intracoronary thrombolysis did not demonstrate these specific arrhythmias. While there is rapid control of injury current with successful intracoronary thrombolysis, Q waves develop rapidly after reperfusion; however, in the days after intracoronary thrombolysis, there is a decline in Q wave with partial regrowth in R wave amplitude in some patients. Thus, specific arrhythmias, most notably accelerated idioventricular rhythm, are useful markers for the occurrence and timing of successful coronary arterial recanalization. In addition, rapid control of injury current and partial regrowth of R waves are electrocardiographic markers of myocardial salvage.