Abstract: Factors related to the initial blood pressure responses to captopril were examined in 82 patients with acute myocardial infarction（AMI）. The results showed that the initial blood pressure responses to captopril in patients with AMI were related to the infarct site, the initial blood pressure level, the status of heart function, the initial level of RAS activity and the time of drug initiation after AMi. RAS reactions to captopril may be the major mechanism for the initial blood pressure responses.