The heart is located behind the breastbone (sternum). The sternum is a long, flat bone situated centrally on the anterior (front) side of the chest. The term “posterior” means “toward the back,” confirming the heart’s position deep within the chest cavity, immediately behind this forward bony structure.
The Direct Anatomical Answer
The heart’s anterior surface, often called the sternocostal surface, sits deep to the sternum and the costal cartilages that connect the ribs. While the sternum runs vertically down the center of the chest, the heart is not perfectly centered behind it. The largest portion of the heart is slightly offset to the left side of the chest.
The superior part of the heart, known as the base, is located near the level of the third costal cartilage. The heart’s inferior tip, the apex, extends further down and to the left, lying near the junction of the fourth and fifth ribs. This positioning places the sternum directly in front of the heart muscle and its major blood vessels.
Understanding the Heart’s Position in the Mediastinum
The heart resides within the mediastinum, the central compartment of the thoracic cavity. This space is located between the two lungs, extending from the sternum in the front to the vertebral column (spine) in the back. The heart is encased by the pericardium, a tough, double-layered membrane that anchors it within the mediastinum.
The outer layer of the pericardium is attached by ligaments to the spinal column, diaphragm, and the sternum. The heart is cone-shaped and oriented obliquely, running from the upper right, downward, forward, and to the left.
This orientation means the heart’s base, formed mostly by the left and right atria, is upward. The apex, formed by the left ventricle, points down and left. The lungs flank the heart, placing it between the sternum anteriorly and the vertebral column posteriorly.
The Sternum’s Role in Protection
The heart’s posterior position relative to the sternum is a fundamental aspect of the body’s natural defense system. The sternum, along with the ribs and costal cartilages, forms the bony thoracic wall, or rib cage. This bony framework creates a rigid barrier for the vital organs housed within the chest.
The primary advantage of this arrangement is protecting the heart and major blood vessels from external trauma. The flat, dense bone of the sternum is effective at absorbing or deflecting direct impact, minimizing the chance of injury to the heart muscle. This shield is important given the heart’s constant, rhythmic motion. The sternum’s location also allows it to be used as a stable platform during procedures like cardiopulmonary resuscitation (CPR) to manually compress the heart.