To investigate initial perfusion status in acute myocardial infarction, methoxyisobutylisonitrile (MIBI) was administered by the rescue physicians. Thirty-nine patients received the radiopharmaceutical at home or upon arrival at the hospital. Diagnosis was confirmed in 30 patients, and 19 emergency thrombolyses were performed. Initial single photon emission tomography (SPET) analysis was constantly abnormal in confirmed myocardial infarction sometimes before direct electrocardiographic signs. MIBI-SPET was normal in non-coronary syndromes. MIBI uptake improved after thrombolysis (P less than 0.001) but also after heparin therapy (P less than 0.05). SPET improvement demonstrated myocardial salvage earlier than wall motion studies. MIBI administration at the patient's home allowed very early perfusion imaging when thrombolysis was performed at home. MIBI-SPET has the potential use of comparing thrombolytic agents or at home versus in hospital thrombolysis.