Twenty-one instances of nonparoxysmal junctional tachycardia (NPJT) were observed in 203 consecutive patients with acute myocardial infarction. The arrhythmia complicated both anterior and inferior wall infarction and was associated with an ominous prognosis, particularly in patients with anteror wall infarction.The NPJT is probably a manifestation of the severity of the lesion. The exact mechanisms of the enhanced A-V junctional activity remain obscure. The possible role of increased levels of epinephrine and norepinephrine and localized increases of potassium in the A-V junction from adjacent necrotic myocardium is suggested.