The pericardium is a thin, double-layered sac that surrounds your heart. It holds the heart in place within your chest, reduces friction as the heart beats, and prevents the heart’s chambers from stretching too far when they fill with blood. In a healthy adult, this sac is no more than 2 mm thick and contains 15 to 50 mL of lubricating fluid, roughly one to three tablespoons.
Layers of the Pericardium
The pericardium has two main layers: a tough outer layer called the fibrous pericardium and a thinner inner layer called the serous pericardium. The fibrous layer is shaped like a cone and anchors the heart to surrounding structures, including the diaphragm below and the large blood vessels above. It’s strong enough to protect the heart from sudden overfilling but flexible enough to allow normal beating.
The serous pericardium is itself split into two sheets. The outer sheet lines the inside of the fibrous layer, while the inner sheet wraps directly around the heart’s surface. That inner sheet is also called the epicardium. Between these two sheets sits the pericardial cavity, a narrow space filled with a small amount of clear fluid. This fluid acts as a lubricant, letting the two surfaces glide against each other with virtually no friction as the heart contracts and relaxes roughly 100,000 times a day.
What the Pericardium Does
The pericardium serves three core functions. First, it anchors the heart in the center of the chest so it doesn’t shift around during movement or changes in body position. Second, its fluid layer eliminates friction between the beating heart and the surrounding tissues. Third, and perhaps most importantly, it acts as a physical restraint that keeps the heart’s chambers from overstretching.
That restraining role matters more than it might sound. When researchers have studied hearts with the pericardium removed, the heart chambers expand more easily under pressure. The pericardium essentially sets an upper limit on how much the ventricles can fill, which helps maintain healthy blood flow between the left and right sides of the heart. This coupling between the two sides is critical: if one ventricle swells too much, it can compress the other, reducing the heart’s overall pumping ability.
Nerve Supply and Pain
The pericardium is supplied by the phrenic nerve, the same nerve that controls the diaphragm. This shared nerve pathway is the reason pericardial problems can produce pain that feels like it’s coming from the shoulder or upper back rather than the chest. Blood reaches the pericardium through a small artery that branches off a larger vessel behind the collarbone and runs alongside the phrenic nerve down to the diaphragm.
Pericarditis: Inflammation of the Pericardium
Pericarditis is the most common disorder of the pericardium. It occurs when the pericardial layers become inflamed, often due to a viral infection, though it can also follow a heart attack, autoimmune disease, or chest trauma. Chest pain is present in over 85% of cases. The pain is typically sharp, sits behind the breastbone, and gets worse when you lie flat, cough, or take a deep breath. Sitting up and leaning forward usually eases it, because that position reduces pressure on the inflamed tissue.
A hallmark finding is a scratchy, squeaky sound a doctor can hear through a stethoscope, caused by the roughened, inflamed layers rubbing against each other. This sound, called a pericardial friction rub, shows up in about one-third of cases. Doctors diagnose pericarditis when at least two of four criteria are present: characteristic chest pain, that friction rub, specific changes on an electrocardiogram, or fluid buildup in the pericardial space. Most cases of acute pericarditis resolve with anti-inflammatory treatment over a few weeks, though some people experience recurrent episodes.
Pericardial Effusion and Cardiac Tamponade
When excess fluid accumulates in the pericardial sac, it’s called a pericardial effusion. Small effusions may cause no symptoms at all. The danger comes when fluid builds up quickly or in large amounts, because the fibrous outer layer of the pericardium doesn’t stretch easily. As fluid fills the sac, it compresses the heart from the outside, leaving less room for the chambers to expand and fill with blood.
If the compression becomes severe enough, it leads to cardiac tamponade, a life-threatening emergency. The heart can no longer pump enough blood to supply the body. Three classic signs appear together: low blood pressure, bulging veins in the neck (because blood backs up when it can’t enter the compressed heart), and muffled heart sounds heard through a stethoscope. Tamponade requires urgent drainage of the fluid to relieve pressure on the heart.
Pericardial Problems After Heart Surgery
Any surgery that opens the pericardium can trigger an inflammatory reaction known as postpericardiotomy syndrome. This typically develops one to six weeks after the procedure and involves new or worsening fluid around the heart or lungs, chest pain, fever, and elevated markers of inflammation in the blood. Overall incidence is around 10%, though it ranges from 2% to 30% depending on the type of surgery. Operations on the aortic valve or aorta carry the highest risk at roughly 26%, while coronary bypass and mitral valve surgeries each trigger the syndrome in about 8% of cases.
Constrictive Pericarditis
In some people, chronic inflammation causes the pericardium to thicken and stiffen over time. Normal pericardial thickness is 2 mm or less on imaging; anything at or above 4 mm is considered abnormal. When the pericardium becomes rigid, it forms a shell around the heart that prevents the chambers from filling properly. Symptoms resemble heart failure: fatigue, swelling in the legs and abdomen, and shortness of breath. Unlike typical heart failure, though, the heart muscle itself is healthy. The problem is entirely mechanical, caused by the stiff casing around it. Severe cases may require surgical removal of the pericardium to restore normal heart function.