Thirty-eight patients underwent left ventricular angiography and coronary arteriography within the first 6 hours of inferior myocardial infarction, in an attempt at intracoronary thrombolysis with streptokinase. Twenty-three of these patients presented with ST segment depression of more than 1 mm on the anterior leads (V1 to V4) of ECGs done immediately before the attempt at thrombolysis (group I), whereas 15 did not (group II). Quantitative analysis of left ventricular angiography showed an ejection fraction significantly lower in group I (51 +/- 10%) than in group II (59 +/- 7%; p less than 0.01). This difference was the result of inferior hypokinesia which was larger both in surface area (group I = 11.5 +/- 6.5 cm2; group II = 4.2 +/- 2.7 cm2; p less than 0.001) and in percentage of ventricular perimeter (group I = 46 +/- 14%; group II = 27 +/- 12%; p less than 0.001). The prevalence of a left anterior descending artery lesion and the degree of stenosis were the same in both groups. The success rate of thrombolysis was not significantly different. However, in cases of persistent success, there was an improvement of regional contraction only in group I, as opposed to absence of change in group II. These results suggest that patients with inferior myocardial infarction and ST anterior depression have an extensive ischemic area rather than anterior wall ischemia. An attempt at coronary thrombolysis seems to be worthwhile only in these patients, as it results in appreciable myocardial salvage when successful.