Which side is the heart on—the left or the right?

The heart is a vital organ in our body. During routine medical check-ups, an electrocardiogram (ECG) is invariably included as a standard examination. Some individuals are uncertain about the precise anatomical location of the heart—whether it lies on the left or right side of the chest. Today, we will clarify the heart’s position.

Is the Heart on the Left or Right Side?

Under normal circumstances, the heart lies slightly to the left of the midline of the sternum. In lay terms, approximately two-thirds of the heart resides in the left side of the thoracic cavity, while the remaining one-third extends into the right side. Rarely, some individuals may have a normally positioned heart located entirely on the right side—a benign anatomical variant rather than a pathological condition. Depending on the configuration of the aorta and major vessels, this can be classified as either dextrocardia or mirror-image dextrocardia. As long as no clinical symptoms are present, such variations are considered physiologically normal. The incidence of this phenomenon is extremely low—less than 1 in 10,000 individuals.

Most people perceive the heartbeat as pulsating on the left side of the chest; however, what they actually feel is the apex of the heart. Structurally, the heart resembles a slightly tilted peach: roughly two-thirds lies to the left of the body’s midline, and one-third lies to the right. The cardiac apex—the most inferior portion of the heart—is where the heartbeat is most prominently palpable, typically located at the intersection of the left fifth intercostal space and the midclavicular line.

Externally, the heart is enveloped by two thin, smooth membranes known as the pericardium. Between these two layers lies a potential space—the pericardial cavity—which contains approximately 20 mL of pale-yellow fluid termed pericardial fluid. This fluid serves a lubricating function during cardiac contraction, minimizing friction and resistance. Additionally, the pericardium provides structural support, preventing excessive cardiac dilation.

Size of the Heart

The human heart is approximately the size of a clenched fist. In adult Chinese males, average heart weight ranges from 234–334 g—roughly equivalent to 0.5–0.7 jin (Chinese unit of weight, ~500 g per jin). In adult females, average heart weight ranges from 209–307 g—approximately 0.4–0.6 jin. Naturally, heart size and weight vary depending on age, height, body weight, and physical fitness.