Previous studies report larger myocardial infarcts and increased in-hospital mortality rates in patients with inferior wall acute myocardial infarction (AMI) and complete atrioventricular block (AV), but the clinical implications of these complications in patients treated with reperfusion therapy have not been addressed. The clinical course of 373 patients--50 (13%) of whom developed complete AV block--admitted with inferior wall AMI and given thrombolytic therapy within 6 hours of symptom onset was studied. Acute patency rates of the infarct artery after thrombolytic therapy were similar in patients with or without AV block. Ventricular function measured at baseline and before discharge in patients with complete AV block showed a decrement in median ejection fraction (-3.5 vs -0.4%, p = 0.03) and in median regional wall motion (-0.14 vs +0.24 standard deviations/chord, p = 0.05). The reocclusion rate was higher in patients with complete AV block (29 vs 16%, p = 0.03). Patients with complete AV block had more episodes of ventricular fibrillation or tachycardia (36 vs 14%, p less than 0.001), sustained hypotension (36 vs 10%, p less than 0.001), pulmonary edema (12 vs 4%, p = 0.02) and a higher in-hospital mortality rate (20 vs 4%, p less than 0.001), although the mortality rate after hospital discharge was identical (2%) in the 2 groups. Multivariable logistic regression analysis revealed that complete AV block was a strong independent predictor of in-hospital mortality (p = 0.0006). Thus, despite initial successful reperfusion, patients with inferior wall AMI and complete AV block have higher rates of in-hospital complications and mortality.