Injury of the radial nerve produced by external compression during dissection of the internal mammary artery during surgery of ischemic heart disease, is an infrequent event. The use of sternal retractors with only one rod may be the cause of these lesions. We report two cases of radial nerve paralysis produced as a consequence of external compression induced by a sternal retractor during dissection of the internal mammary artery. In the first case the patient showed loss of power of the external muscles of the left forearm and a clear flexion of the left hand. The second patient presented loss of power of the left hand and impossibility to extend the carpus and fingers. In both cases the lesion was reversible.