To compare nuclear magnetic resonance (NMR) image-derived T1 and T2 changes during evolving infarction, 14 dogs were studied serially: (1) 1 to 2 hours after left anterior descending coronary occlusion, (2) 2 to 3 hours after coronary occlusion (n = 7) or in the first hour after reperfusion following 2 hours of occlusion (n = 7), and (3) 5 days and (4) 21 days after occlusion/reperfusion. In addition, the extent of T1 and T2 abnormalities was compared to the extent of infarction as determined histologically for each set of images. With sustained coronary occlusion, an increase versus control values (T1 = 351 +/- 11 msec; T2 = 41 +/- 2 msec) was observed in the second hour after occlusion (T1 = 448 +/- 51 msec; T2 = 51 +/- 8 msec), gradually reaching a maximum by day 5 (T1 = 490 +/- 64 msec; T2 = 63 +/- 9 msec). By 21 days, T1 had decreased to 427 +/- 43 msec and T2 to 55 +/- 11 msec. However, with myocardial reperfusion, an abrupt increase in both T1 and T2 occurred compared to prereperfusion values in the first hour after release of occlusion, from 445 +/- 32 msec to 555 +/- 65 msec and from 52 +/- 5 msec to 65 +/- 8 msec, respectively. Subsequently, T1 remained elevated whereas T2 normalized. Only on day 21 images was there a good correlation between the extent of T1 and T2 abnormalities and infarct size, in both nonreperfused (r = 0.87; p less than 0.05), and reperfused (r = 0.89; p less than 0.01) dogs.(ABSTRACT TRUNCATED AT 250 WORDS)