The heart is often mistakenly believed to be located entirely on the left side of the chest. While the answer is nuanced, the heart is actually situated centrally within the chest cavity. The perception of the heart being exclusively on the left stems from its orientation and the location of its strongest beat. It is positioned between the lungs, slightly behind and to the left of the breastbone (sternum).
The Heart’s True Anatomical Position
The heart is housed within the thoracic cavity, nestled between the two lungs and resting upon the diaphragm. It is positioned posteriorly to the sternum and anteriorly to the vertebral column. The heart is not a symmetrical organ; its mass is distributed unevenly across the body’s midline.
Approximately two-thirds of the heart’s total mass lies to the left of the midline, while the remaining one-third is situated on the right. The heart’s broad upper portion, known as the base, points generally toward the right shoulder, where the great blood vessels attach. Conversely, the pointed lower tip, called the apex, is directed downward, forward, and distinctly to the left. This apex typically lies near the junction of the fourth and fifth ribs, just to the left of the sternum.
Why It Seems to Be on the Left Side
The popular belief that the heart is entirely on the left is influenced by where the strongest cardiac activity is felt. This dominant sensation is caused by the apex beat, also called the point of maximal impulse (PMI), which is the palpable thrust of the heart’s apex against the chest wall during contraction. This beat is usually felt in the fifth intercostal space, along the midclavicular line, far to the left of the sternum.
The left ventricle is primarily responsible for generating this powerful impulse. This chamber pumps oxygenated blood to the entire systemic circulation, requiring it to generate significantly more pressure than the right ventricle. Consequently, the muscular wall of the left ventricle is about three times thicker than the right ventricular wall, typically measuring 8 to 12 millimeters compared to the right’s 3 to 5 millimeters. The powerful movement of the left ventricular apex creates the distinct impulse felt on the left side of the chest.
The Role of the Mediastinum in Central Placement
The heart’s location is anatomically defined by the space it occupies: the mediastinum. This is the central compartment of the thoracic cavity, situated between the two lungs. Its boundaries are the sternum in the front, the vertebral column in the back, and the diaphragm muscle below.
The heart, enclosed in its protective sac called the pericardium, is located within the middle part of the inferior mediastinum. Other major structures that share this central space include the trachea, the esophagus, major blood vessels like the aorta, and various nerves and lymph nodes. Placing the heart in the mediastinum confirms its status as an anatomically central organ, protected by the surrounding rib cage and sternum despite its slight leftward tilt.