One hundred thirty-one patients presenting with acute myocardial infarction (AMI) a mean of 3 hours after the onset of symptoms were treated with oral aspirin and intravenous thrombolytic therapy followed by heparin. One hundred eleven patients (85%) also received intravenous followed by oral beta blockers. Twenty-one patients (19%) discontinued the beta blocker because of complications. Five (4.5%) required the addition of diuretic drugs or converting enzyme inhibitors. Six patients (5%) discontinued the beta blocker after complete mechanical revascularization, and 1 patient was noncompliant. Long-term treatment continued in 90 patients (69%) over a 2-year follow-up period (average 13 months). There were 3 infarct extensions and 3 reinfarctions (5%). Overall mortality at 2 years was 10%. Intravenous beta blockers are well tolerated in most patients treated with thrombolytic agents, aspirin and heparin. They may further improve the survival benefit of chronic beta blocker therapy in the period after AMI.