The chest wall is made up of the ribs and the muscles between the ribs. The lungs are separated by the mediastinum mediastinumThe space in the chest between the lungs, breastbone and spine that contains the heart, great blood vessels, thymus, trachea (windpipe), esophagus and lymph nodes., which contains the heart and other organs.Below the lungs is the diaphragm, a thin muscle that separates the chest cavity from the abdomen. Each lung is divided into lobes (sections): 1  The left lung has 2 lobes. which contains the heart and other organs. Below the lungs is the diaphragm, a thin muscle that separates the chest cavity from the abdomen. Each lung is divided into lobes (sections): 1  The left lung has 2 lobes.