The heart is protected by the rib cage, which is a bony structure formed by the ribs, sternum (breastbone), and thoracic vertebrae (bones of the spine). The inferior tip of the heart, called the apex, lies just to the left of the sternum between the junction of the fourth and fifth ribs near their articulation with the costal cartilages.
Therefore, the fourth and fifth ribs are primarily responsible for covering the heart.
