To search for electrocardiographic clues of infarction of the right ventricle, we recorded the right-thoracic unipolar leads from V3R to V6R and the following abdominal leads: MD, ME and MI, in a group of 40 normals (control group) and in a group of 40 patients with their first acute transmural myocardial infarction (25 posterior-inferior, 15 anterior wall). We described the predominant ECG morphologies in the control waves (more than 0.04 sec. duration) could be registered in the right anterior thoracic wall in healthy subjects. Based on the findings from our control group and those reported from other investigators, we concluded that to suspect right ventricular involvement in the above mentioned leads, it is required to find necrosis and subepicardial injury waves in at least two of those leads. The most frequently affected leads were V4R and MD. This electrocardiographic "positive" pattern to suspect involvement of the right ventricle was found in 32% of the posterior-inferior left ventricular infarctions. In none of the left ventricular anterior wall infarctions we observed right-sided involvement. The clinical-electrocardiographic correlation was statistically significant. Due to the hemodynamic and therapeutic consequences when right ventricular involvement is suspected, it is convenient to record, in every patient with posterior-inferior myocardial infarction, the special leads described above, more so since the ECG is a simple fast, low cost invaluable auxilliary in the evaluation of the extension of necrosis in the right ventricle.