Inside the left rib cage are mainly the organs of the left thoracic cavity, some of the organs of the midline mediastinum, and the organs of the left upper abdomen. The thoracic organs include the lung lobes and the heart on the left side. In most people, the heart is located on the left side, and in a small number of people, the heart can appear as a mirror image and be located on the right side. Some of the mediastinal organs are seen in the middle of the left chest wall and include the large blood vessels of the heart, the esophagus, and the lymphatic vessels and lymph glands. The organs of the left upper abdomen are the stomach, pancreas, and part of the duodenum, as well as the spleen, which is located on the posterior abdominal wall. Pain or symptoms in the left chest wall may also be due to problems with the organs inside the left chest wall, resulting in reflex pain. Therefore, when there is pain or abnormalities in the left chest wall, it is also important to consider the diseases of the organs contained within it.