The rib cage protects the thoracic cavity which contains: the heart and the great vessels (The thoracic aorta, the pulmonary artery and its branches, the pulmonary veins, the azygos vein, the superior and a portion of the inferior vena cava)
It also contains the trachea, the bronchi, the lungs, the esophagus, the sympathetic chains, the thoracic duct, and the thymus gland.