OBJECTIVE: To assess the efficacy of early accelerated dose tissue plasminogen activator on in-hospital patency of the infarct related artery in patients with inferior myocardial infarction with and without right ventricular involvement. DESIGN: Single centre prospective assessment before discharge of infarct related vessel patency after early thrombolysis. SETTING: Tertiary cardiac referral centre at a university hospital. PATIENTS AND METHODS: 90 consecutive unselected patients with acute myocardial infarction, of whom 35 (39%) had electro-cardiographic evidence of right ventricular involvement (ST segment elevation greater than 0.1 mV in right precordial lead V4R), were studied. All patients received accelerated dose tissue plasminogen activator 100 mg within six hours from the onset of symptoms and had control angiography before discharge. MAIN OUTCOME MEASURES: Infarct related coronary artery patency using the Thrombolysis in Myocardial Infarction (TIMI) grading system before discharge. Incidence of prolonged systemic hypotension, sinus bradycardia, complete atrioventricular block, and ventricular tachyarrhythmia during early hospitalisation. RESULTS: Despite aspirin and bolus heparinisation before thrombolysis and high dose heparinisation thereafter for at least 48 hours the infarct related artery was more likely to be occluded (TIMI 0 or 1 flow) in patients with right ventricular involvement than in those without (69 v 29%, P < 0.001), as shown by control angiography performed a mean of 12.8 days after thrombolysis. These findings may be explained, at least in part, by predominant involvement of the proximal right coronary artery (66 v 31%, P < 0.05) and a low cardiac output syndrome, being indirectly reflected by a high incidence of prolonged hypotension (26 v 7%, P = 0.02), bradycardia (34 v 14%, P = 0.03), and complete atrioventricular block (37 v 5%, P = 0.0001). CONCLUSION: Primary angioplasty should be considered as the treatment of choice in patients with acute inferior infarction with right ventricular involvement because of the high failure rate of thrombolysis.