The sternalis muscle (SM) is an anatomical variant found in the anterior thoracic wall. While the attachment sites of SM are generally agreed upon, the innervation and function of this muscle are not well established. Cadaveric and surgical explorations to date report that SM is innervated by either the pectoral nerves or the anterior branches of the intercostal nerves, or a combination of both. Knowledge of SM is relevant to health care providers specialising in imaging and/or surgery of the anterior thoracic wall. This paper aims to raise awareness in the medical community of the clinical relevance of SM through two case reports and a brief literature review.