The rectus thoracis muscle is an often forgotten but rare muscular variation of the anterior thoracic wall. This muscle variant appears in about 8% of the population and is a result of embryological variation. The muscle variant appears to have no apparent physiological activity except for possible proprioception and respiration functions. The lack of physiological activity can alter electrocardiogram readings. Increased awareness and thorough knowledge of anatomical variants with clinical significance is imperative to minimizing risks of surgical complications. This report displays the finding of the rectus thoracis muscle on the right pectoral region in a 78-year-old male cadaver. In addition to the embryological reasoning, the presence of rectus thoracis has a tendency to cause clinical misinterpretation of mammogram and electrocardiogram readings. Myocardial infarctions can cause trigger points to develop within the rectus thoracis, which can manifest into longstanding chest pain.
