Many vital organs and tissues are located in the chest cavity, such as the heart lungs, esophagus, trachea, and large blood vessels, and the chest wall protects these vital organs and tissues. Both breasts are located on the outside of the chest wall, and the heartbeat can be touched through the middle of the left breast. There are no major organs or tissues underneath the breasts, and all of the important thoracic tissues of the chest are within the chest cavity. In fact, the text should be referring to the organ behind the left breast, which also refers to the heart, that is, the organ inside the chest wall behind the left breast is the heart.