The intensity of 111In antimyosin uptake is related to the type (Q wave or non-Q wave), size, and location of an acute myocardial infarction. To determine whether the uptake intensity is also related to the infarct age, and to establish the time frame during which 111In antimyosin uptake occurs postinfarction, we studied a quantitative measure of uptake intensity, the heart-lung (HL) ratio, in 90 consecutive patients at various intervals following a Q wave infarction. Imaging was performed 24 hours following 111In antimyosin injection. Uptake of antimyosin could be demonstrated up to 154 days postinfarction. The HL ratio was measured as the ratio of the maximum counts in the infarcted myocardium to the adjacent lung background, and was 1.93 +/- 0.51 (mean +/- SD) overall. The ratio declined exponentially with increasing age of infarct. Using nonlinear regression analysis, 47% of the total variance of the HL ratio could be attributed to age alone (p less than 0.001). Sequential antimyosin imaging was performed in nine patients, with the first study between 4 and 15 days, the second between 50 to 100 days, and the third between 125 to 270 days after the onset of chest pain. The HL ratios were (mean +/- SD) 1.77 +/- 0.25 for scans between 4 and 15 days, 1.54 +/- 0.12 for scans between 50 and 100 days (p less than 0.02), and 1.42 +/- 0.16 (p less than 0.05) for scans between 125 to 270 days, further establishing the progressive reduction in 111In antimyosin uptake with age of myocardial infarction.