Where Is the Heart Located in Relation to the Diaphragm?

The heart sits directly above the diaphragm, resting on it. More precisely, the bottom surface of the heart, called the inferior or diaphragmatic surface, lies against the central tendon of the diaphragm, separated only by the fibrous pericardial sac that encloses the heart. This positioning means the two structures are not just neighbors but physically coupled, and the diaphragm’s constant motion during breathing tugs, pushes, and shifts the heart with every breath you take.

The Physical Arrangement

The diaphragm is a broad, dome-shaped sheet of muscle and tendon that separates the chest cavity above from the abdominal cavity below. Its central portion, the central tendon, is a flat fibrous plate that does not contract. The heart, enclosed in its pericardial sac, rests on this central tendon. The pericardium is actually fused to the upper surface of the central tendon, so the heart does not simply float above the diaphragm; it is tethered to it.

Because the heart is oriented slightly to the left and tilted forward, most of this contact occurs on the left side of the central tendon. The left ventricle, which is the thickest and most muscular chamber, forms the bulk of the heart’s underside where it meets the diaphragm. The right ventricle also contributes to this inferior surface, but to a lesser extent. If you could look up through the diaphragm from the abdomen, you would see the heart’s silhouette pressing down slightly into the tendon, with the liver pushing up from below on the right side and the stomach and spleen sitting beneath the left.

Why the Phrenic Nerves Matter

The nerves that control the diaphragm, the left and right phrenic nerves, travel from the neck downward through the chest in close contact with the heart itself. The right phrenic nerve descends along the lateral surface of the right atrium and right ventricle before passing through the diaphragm at the opening for the vena cava, at roughly the level of the eighth thoracic vertebra. The left phrenic nerve runs down the front of the pericardial sac over the left ventricle and terminates at the central tendon of the diaphragm.¹

This intimate path has real consequences. During heart surgery, the phrenic nerves can be injured by cold cardioplegia solutions, retraction, or direct surgical trauma. When a phrenic nerve is damaged, that half of the diaphragm becomes partially or fully paralyzed, which reduces your breathing capacity. It also means that conditions affecting the heart, such as pericarditis or cardiac surgery, can indirectly compromise diaphragm function, and vice versa. The nerves serve as a literal wiring link between the two organs.

How Breathing Moves the Heart

Because the heart is attached to the diaphragm, every breath shifts the heart’s position inside the chest. When you inhale, the diaphragm contracts and flattens downward. This pulls the heart slightly downward and changes its orientation. When you exhale, the diaphragm relaxes back up into its dome shape, and the heart rides upward with it. The movement is not trivial. MR imaging studies have shown that the heart does not return to the exact same position from one heartbeat to the next during breathing, and the margins of the heart shift inward during suspended respiration.²

Researchers have also tracked how the coronary arteries move in relation to diaphragm motion during free breathing. The displacement of the left main coronary artery correlates with the motion of the right diaphragm, but the relationship varies enormously from person to person. In one real-time MRI study, the correlation slopes ranged from 0.17 to 0.93 across volunteers, meaning that in some people the heart tracks the diaphragm’s motion closely and in others it moves relatively independently.³

This variability matters in medical imaging and radiation therapy. When a technician asks you to hold your breath during a cardiac MRI or CT scan, it is partly because they need the heart to stay still long enough to get a clear picture. But even a breath hold does not perfectly freeze the heart in place. Anyone planning targeted radiation near the heart, as happens in some breast or lung cancer treatments, has to account for the fact that the heart wanders with breathing and that the amount of wandering differs from patient to patient.

The Diaphragm as a Cardiac Pump

The diaphragm does more than just sit beneath the heart. Its contractions actively help the heart fill with blood. When the diaphragm descends during inhalation, it lowers the pressure inside the chest cavity. That drop in pressure is transmitted across the thin walls of the right atrium, effectively pulling blood from the large veins into the heart. At the same time, the descending diaphragm raises pressure in the abdomen, squeezing abdominal veins and pushing blood upward toward the chest.⁴

This mechanism, sometimes called the respiratory pump or abdominal muscle pump, supplements the heart’s own pumping action. In healthy people, deliberately using abdominal (diaphragmatic) breathing increases the volume of blood returning to the heart, which in turn increases the amount of blood the left ventricle ejects with each beat and raises overall cardiac output.⁵ This is one reason breathing exercises and diaphragmatic breathing techniques are recommended for people recovering from heart failure or dealing with poor circulation in the legs. The diaphragm is not just a breathing muscle; it is an accessory to the circulatory system.

Exercise and the Competition for Blood Flow

During intense exercise, the relationship between the diaphragm and the heart gets more complicated. The diaphragm is a skeletal muscle, and like your leg muscles, it needs blood flow to keep working. At very high exercise intensities, the diaphragm can fatigue, and when it does, a reflex kicks in that increases sympathetic nervous system activity. This reflex constricts blood vessels in the limbs, redirecting blood flow away from the legs and toward the overworked respiratory muscles.⁶

The practical result is a tug-of-war between your breathing muscles and your locomotion muscles for a limited supply of blood from the heart. If you have ever hit a wall during hard running where your legs seemed to give out even though you felt like you could keep breathing, this competition for cardiac output may be part of the explanation. Training the diaphragm’s endurance, which is the premise behind inspiratory muscle training devices, aims to raise the threshold at which this reflex kicks in, potentially preserving more blood flow for the legs.

When the Boundary Breaks Down

The most dramatic example of the heart-diaphragm relationship going wrong is congenital diaphragmatic hernia, or CDH. In this condition, a hole in the diaphragm allows abdominal organs like the intestines, stomach, or liver to push upward into the chest cavity during fetal development. These herniated organs crowd the developing lungs and can physically displace and compress the heart. In many CDH cases, the heart is shifted to one side, a condition called cardiac malposition, and the degree of that shift can persist even after surgical repair.⁷

The cardiac effects of CDH go beyond simple displacement. The mass of herniated organs pressing against the developing heart can restrict growth of the left-sided heart structures, leading to a smaller left ventricle with reduced pumping capacity. Reduced blood flow reaching the left side of the heart during fetal life, caused by redirection of normal circulatory patterns, compounds this underdevelopment.⁸ This is a vivid illustration of how dependent the heart is on its relationship with the diaphragm: disrupt the barrier between chest and abdomen, and the heart’s development and function can suffer profoundly.

A much rarer variant is a peritoneopericardial communication, where the defect in the diaphragm’s central tendon opens a direct channel between the abdominal cavity and the pericardial sac around the heart. In one reported case, an 81-year-old man was found to have omentum, the fatty tissue draping the intestines, herniated through such a defect and sitting inside the pericardial space directly in front of the heart.⁹ Cases like this underscore just how thin the boundary between the heart and the abdomen actually is. A defect of a few centimeters in the central tendon can erase the separation entirely.

Referred Pain and Diagnostic Confusion

The physical proximity and shared nerve pathways between the heart and the diaphragm create a well-known diagnostic headache: referred pain. Pain signals from the heart and pain signals from the diaphragm converge on the same relay neurons in the spinal cord. Research in primates has documented that a majority of the spinal cord neurons receiving input from the phrenic nerve (which serves the diaphragm) also receive input from cardiopulmonary sensory nerves.¹⁰

This convergence explains why diaphragm irritation can feel like heart pain and, less commonly, why cardiac problems can be mistaken for abdominal or shoulder issues. Classic examples include:

Shoulder pain from diaphragm irritation: Air trapped under the diaphragm after laparoscopic surgery, or blood pooling against the diaphragm after a ruptured spleen, often causes sharp pain in the shoulder tip. The phrenic nerve originates from the same spinal levels (C3-C5) that supply sensation to the shoulder, so the brain misinterprets the signal.
Upper abdominal pain from a heart attack: Inferior wall heart attacks, which involve the bottom surface of the heart resting on the diaphragm, can present with pain that feels like severe indigestion or an abdominal problem rather than classic chest tightness.
Chest pain from a subdiaphragmatic abscess: An infection just below the diaphragm can irritate it from underneath, producing chest pain and even a small pleural effusion above, mimicking a lung or cardiac condition.

Clinicians are trained to consider these overlapping pain patterns, but patients are often surprised that a problem clearly located in one part of the body can produce symptoms felt in a completely different region. The shared wiring between the heart and the diaphragm is one of the most common reasons for this kind of misdirection.

How Surgeons Navigate the Heart-Diaphragm Interface

When doctors need to drain fluid from around the heart, a procedure called pericardiocentesis, the proximity of the diaphragm is front and center in planning. In the most common approach, a needle is inserted just below the sternum and angled upward toward the left shoulder, passing through a small gap between the diaphragm and the bottom of the heart. The diaphragm is millimeters below the target. CT reconstructions of drainage tube paths after anterior pericardiocentesis have confirmed that the tubes curve through this narrow space without actually penetrating the diaphragm or entering the abdominal cavity.¹¹

This requires precision. If the needle goes too low or at the wrong angle, it can puncture the diaphragm and enter the peritoneal cavity, risking injury to the liver or other abdominal organs. If it goes too far into the pericardial space, it can nick the heart itself. Modern pericardiocentesis is almost always guided by echocardiography or fluoroscopy to visualize exactly where the needle tip is in relation to the heart and diaphragm. The procedure is a practical demonstration of how tightly these two structures are packed together: the margin for error is measured in millimeters.

Open-heart surgery involves similar considerations. When the sternum is split and the chest is opened, surgeons must carefully free the pericardium from the diaphragm’s surface if they need access to the inferior heart. In some cardiac operations, the diaphragm itself is intentionally incised to gain access to structures below, and in those cases the phrenic nerves, running right along the lateral edges of the pericardium, must be identified and protected. Damage to a phrenic nerve during cardiac surgery remains one of the recognized complications, and it can leave a patient with a permanently elevated hemidiaphragm and reduced lung capacity on that side.

Why the Heart Sits Where It Does

The heart’s position above the diaphragm is not an accident of anatomy but a functional arrangement with real physiological advantages. Sitting atop the diaphragm gives the heart a stable platform that moves in a predictable, rhythmic way with breathing. The respiratory pump effect described earlier depends entirely on this arrangement: if the heart were suspended in the middle of the chest without diaphragmatic contact, the pressure changes from breathing would be far less effective at driving venous return.

The diaphragm also acts as a partial shock absorber. Abdominal organs like the liver, stomach, and intestines are separated from the heart by this muscular wall, which means that ordinary activities like eating a large meal, getting punched in the gut, or bearing down during heavy lifting transmit force to the diaphragm rather than directly to the heart. The diaphragm flexes and absorbs some of that mechanical energy. In conditions where this barrier is compromised, as in diaphragmatic hernias, the heart becomes vulnerable to direct compression from abdominal contents, and the results can be severe.

Even the shape of the diaphragm contributes. Its dome curves upward higher on the right side, where the liver pushes it up, and somewhat lower on the left, leaving a natural recess where the heart sits slightly tilted. This asymmetry complements the heart’s own leftward tilt and ensures that the two organs nestle together efficiently without one compromising the other’s function. When people say the heart sits “in the middle of the chest, slightly to the left,” the leftward positioning is partly a consequence of the diaphragm’s own asymmetric shape creating space on the left side for the heart’s apex to point toward.

Hiccups, Spasms, and the Heart Connection

Hiccups are involuntary spasms of the diaphragm, and while they are usually harmless, persistent or intractable hiccups can occasionally signal cardiac problems. Pericarditis, tumors near the diaphragm, or even a pericardial effusion pressing on the diaphragm’s surface can trigger hiccups that will not stop. The mechanism is straightforward: anything irritating the diaphragm or the phrenic nerve can provoke spasmodic contractions.

More commonly, people notice a vague awareness that their heart and breathing feel connected. If you have ever felt your heart “skip a beat” when you take a very deep breath, or noticed that your heart rate speeds up when you inhale and slows when you exhale, you are feeling the consequences of the heart sitting on the diaphragm. The heart-rate fluctuation tied to breathing, called respiratory sinus arrhythmia, is considered normal and is actually a sign of a healthy autonomic nervous system. It is most pronounced in younger, fit individuals and tends to diminish with age. Part of this response is neurally mediated through the vagus nerve, but the mechanical coupling between the diaphragm and the heart contributes as well: changes in thoracic pressure during breathing physically alter how much blood enters the heart from moment to moment, and the heart rate adjusts accordingly.