The human heart is a four-chambered muscular pump situated within the chest cavity, slightly to the left of the midline. Its anatomical position is tilted, requiring specialized terminology to describe its surfaces. Anatomists use the terms “base” and “apex” to define the heart’s superior and inferior ends. This clarifies the heart’s orientation and the relationship between its major chambers and the large blood vessels connected to it.
Understanding the Base and Apex
The terms “base” and “apex” in heart anatomy are often counter-intuitive because the base is located at the top of the organ, and the apex is the pointed tip at the bottom. This conceptualization comes from viewing the heart as an inverted pyramid or a cone lying on its side. The broad, flatter surface is considered the base, while the narrow, tapering end is the apex.
The base represents the superior, posterior surface of the heart, forming the anchor point for the large vessels that transport blood. The apex is the rounded, inferior-most projection formed by the tip of the left ventricle. This distinct orientation means the heart’s long axis runs diagonally from the base (upward, backward, and right) toward the apex (downward, forward, and left).
Precise Anatomical Location
The base of the heart is situated within the mediastinum, the central compartment of the thoracic cavity located between the lungs. It forms the heart’s posterior surface, pressing against the structures in front of the vertebral column. This location is directed superiorly, posteriorly, and slightly toward the right side of the body.
Anteriorly, the base is positioned at the level of the third costal cartilage, which connects the third rib to the sternum. Posteriorly, the base aligns with the bodies of the fifth through eighth thoracic vertebrae (T5–T8). It is separated from the vertebrae by structures including the esophagus, the thoracic duct, and the descending aorta.
Major Structures Composing the Base
The base is structurally defined by the superior receiving chambers and the great vessels that attach to them. The bulk of the base is formed primarily by the posterior surface of the left atrium, with a smaller portion contributed by the right atrium.
The defining feature of the base is the collection of large blood vessels that enter or exit the heart at this superior pole. These great vessels include the superior vena cava and the inferior vena cava, which drain into the right atrium. Additionally, the four pulmonary veins, which return oxygenated blood from the lungs, connect directly into the posterior left atrium. The presence of these large, anchoring vessels creates the broad, quadrilateral structure referred to as the base.