For purposes of evaluating the clinical features in the prehospital phase of acute myocardial infarction, 22 patients presenting prehospital syncope and patients presenting in-hospital re-attack were chiefly studied. Cardiac or ventricular standstill, acute mechanical failure, ventricular fibrillation, serious block, bradycardia-hypotension syndrome, cardiogenic shock, cardiac failure and cardiac rupture may be cited as the complications likely to occur in the early phase of the onset of acute myocardial infarction. Among these complications, cardiac or ventricular standstill results from overactivity of the vagus nerve, and acute mechanical failure is a result of drastically decreased cardiac output due to extensive infarction. There is no report of either complication, and both may be considered to be the fatal complications occurring almost simultaneously with the onset of acute myocardial infarction. The time intervals from the onset of symptoms to hospital admission were perspectively analyzed on 72 patients transported by the MCCU and 139 by ordinary ambulance. The interval from the onset of symptoms to medical help and that from the examination by personal physician to the call for ambulance were the greatest of all time factors, while the interval for emergency transport of the patient was short. There was no significant difference in the interval to hospital admission between the patients transported by the MCCU and those by ordinary ambulance. However, the in-transit death rate was 1/72 patients transported by the MCCU and 8/139 by ordinary ambulance: in other words, this death rate tended to be high in the latter. Twenty-two normal volunteers were studied for changes in heart rate, blood pressure and double product with the speed of transport. The transport at a low speed caused less changes in these parameters than that at a high speed.