The heart is a muscular pump situated within the chest cavity, positioned behind the breastbone and between the lungs. The body’s interior geography is complex, with several vital organs nestled immediately below or behind the heart, primarily residing in the upper abdominal region. Understanding this close proximity is important because issues in these adjacent organs can sometimes feel like they originate in the heart itself. To understand what lies beneath the heart, one must first look at the muscular sheet that forms the floor of the chest and separates the thoracic contents from the abdominal contents.
The Floor of the Chest Cavity: The Diaphragm
The diaphragm is a large, dome-shaped sheet of skeletal muscle that forms the physical boundary between the chest cavity and the abdominal cavity. This structure is the primary muscle for breathing, working by contracting and flattening to draw air into the lungs. The heart rests immediately above the central tendon of the diaphragm, which is a flat, fibrous sheet near the center of the dome. This muscle’s function of separating the thorax from the abdomen defines which organs are truly “under” the heart. The diaphragm is slightly asymmetric; its right half sits higher than the left because of the massive liver directly beneath it. The diaphragm contains openings, called hiatuses, that allow structures like the esophagus and major blood vessels to pass between the two body cavities.
Immediate Neighbors: The Stomach and Esophagus
The esophagus is a muscular tube responsible for transporting swallowed food down to the stomach. It descends through the chest cavity and passes through a small opening in the diaphragm, known as the esophageal hiatus, just before it connects to the stomach. The stomach itself is located in the upper left quadrant of the abdomen, sitting immediately beneath the left side of the diaphragm. The uppermost section of the stomach, called the fundus, is often positioned quite high, directly adjacent to and below the heart.
Digestive Pain Mimicry
The close anatomical relationship of the esophagus and the upper stomach to the heart and its nerves means that pain originating from digestive issues, such as severe acid reflux or spasms, can sometimes mimic cardiac pain. The lower esophageal sphincter, a ring of muscle at the junction of the esophagus and stomach, is functionally assisted by the diaphragm muscle fibers that encircle it, helping to prevent acidic contents from refluxing back up.
The Largest Structure: The Liver
The liver is the largest solid organ in the human body, typically weighing between three and four pounds in an adult. It occupies the majority of the upper right quadrant of the abdomen, positioned directly beneath the right half of the diaphragm. Due to its sheer size, the liver extends across the midline, sitting below and slightly to the right of the heart’s lower chambers. Its large, convex superior surface is contoured to fit against the underside of the diaphragm. The liver performs many functions, including regulating chemical levels in the blood, processing nutrients, and metabolizing toxins. It also produces bile, which is essential for digestion. The liver’s location directly underneath the diaphragm emphasizes its importance in processing all the blood returning from the stomach and intestines before it circulates to the rest of the body.
Supporting Systems: Spleen and Great Vessels
The spleen is located high in the upper abdomen, positioned on the far left side, tucked behind the stomach and under the protective cover of the diaphragm and the lower ribs. This organ functions primarily as a blood filter and a component of the immune system, lying in very close proximity to the heart’s lower left border. The great vessels are also functionally located “under” the heart as they connect the upper and lower halves of the circulatory system. The aorta descends from the heart, passing behind the diaphragm to carry oxygenated blood down to the lower body and limbs. The inferior vena cava collects deoxygenated blood from all structures below the diaphragm and passes through a central opening to empty directly into the right side of the heart.