The aim of this study was to investigate the correlation between the ST-segment and T-wave patterns in predischarge electrocardiogram and patency of left anterior descending coronary artery in patients with a first anterior myocardial infarction (AMI). One hundred and fifty-six of 175 consecutive patients who were admitted to our clinic between January 2000 and September 2002 due to a first episode of transmural AMI and who received thrombolytic therapy were enrolled. Coronary angiography was performed by the Judkins method on the 6th-10th day after the acute infarction. The corrected TIMI frame count (CTFC) was estimated according to the previously described method. According to the combination of the ST-segment and T-wave morphology on the day (6-10) of cardiac catheterization, patients were classified into four groups: group A, ST elevation <<0.1 mV and negative T waves; group B, ST elevation >or=0.1 mV and negative T waves; group C, ST elevation <<0.1 mV and positive T waves; and group D, ST elevation >or=0.1 mV and positive T waves. Of the 99 patients with negative T waves, 47 (48%) had CTFC <or=27, 32 (32%) CTFC between 27 and 40, 15 (15%) CTFC >or=40-100, and 5 (5%) CTFC >>100. Of the 57 patients with positive T waves, CTFC was <or=27 in 14 (25%), between 27 and 40 in 17 (30%), >or=40-100 in 11 (19%), and >>100 in 15 (26%) ( P << 0.001). From the 76 patients with an isoelectric ST segment, 38 (50%) had CTFC <or=27, 29 (38%) CTFC between 27 and 40, 8 (11%) CTFC >or=40-100, and 1 (1%) CTFC >>100. Of the 80 patients with an elevated ST segment, 23 (29%) had CTFC <or=27, 20 (25%) CTFC between 27 and 40, 18 (23%) CTFC >or=40-100, and 19 (23%) CTFC >>100 ( P << 0.001). Use of the combination of two electrocardiographic parameters (ST segment and T waves) also indicated that there were significant differences between groups A and D, and groups B and D ( P << 0.001 and P << 0.05, respectively). Development of an isoelectric ST segment with negative T waves may indicate a better degree of reperfusion after AMI. In contrast, patients in whom ST-segment elevation and positive T waves remain at discharge from the coronary care unit have a higher probability of a nonpatent left anterior descending artery.