In 20 patients with acute myocardial infarction (AMI), serial Tl-201 myocardial scintigraphy was performed and scintigraphic infarct size (SIS) was determined 1 (or less), 2 and 8 weeks after AMI. Hemodynamic indices were determined with a Swan-Ganz catheter at a mean of 27.7 hours after AMI. Left ventricular ejection fraction (EF) was determined with Tc-99m HSA cardiac blood pool scintigram at 8 weeks after AMI. Mapping ECG was also observed serially. Of 20 patients, SIS decreased in 12, was unchanged in 2 and increased in 5 . No image defect was observed on the initial scintigram in one case. When the patients were classified into two groups, i.e. those with initial SIS more than 25% and those with initial SIS less than 25%, hemodynamic indices were demonstrated to be more markedly impaired in the former than in the latter. However, when all patients were pooled, correlations between the initial SIS and hemodynamic indies (CI, SI, SWI, PADP) were poor. There was a good correlation between SIS and EF both determined 8 weeks after AMI. When the patients were clasified into the improved and unimproved groups according to the per cent change of SIS (CIS), both hemodynamic indies on admission and EF at 8 weeks were better in the improved than in the unimproved group, and especially significant correlation was found between CIS and each of SI and PADP. There was a good correlation between maximum ΣST in mapping ECG and SIS at 1 week after AMI. From these results, it is suggested that a decrease in SIS in serial Tl-201 myocardial scintigrams represents the presence of transiently ischemic area and that serial Tl-201 myocardial scintigraphy performed from the initial stage after AMI may provide a useful information for evaluating the effect of therapeutic intervention and predicting the prognosis.