A pericardial fat pad is a collection of fatty tissue in and around the sac that surrounds your heart. It’s a normal anatomical structure that everyone has to some degree, typically appearing at the front of the heart where it meets the diaphragm. Most people learn about it after seeing the term on a chest X-ray or CT scan report, and in the majority of cases, it’s an incidental finding that requires no treatment.
Where Pericardial Fat Sits
Your heart is enclosed in a double-layered sac called the pericardium. Fat can accumulate in several spots within and around this sac. The term “pericardial fat pad” is used broadly to describe all of this fatty tissue collectively, but technically, the fat falls into two distinct categories based on its exact location.
Epicardial fat sits directly on the heart’s outer surface, sandwiched between the heart muscle and the inner lining of the pericardial sac. It tends to collect along the coronary arteries and in the groove between the heart’s upper and lower chambers. This fat shares its blood supply with the heart muscle itself, which is part of why researchers pay close attention to it.
The second type accumulates outside the heart’s surface layer but still within or just anterior to the pericardial sac. Additional fat can also build up in the surrounding chest cavity (the mediastinum), particularly in front of the right side of the heart. When doctors refer to a “pericardial fat pad” on imaging, they’re usually describing the combined effect of these fat deposits filling in the space at the front lower corner of the heart, known as the cardiophrenic angle.
What It Looks Like on Imaging
On a standard chest X-ray, the pericardial fat pad appears as a soft, rounded shadow at the front of the heart, most visible on the lateral (side) view. Depending on the person’s body type and the angle of the X-ray, it can show up as a well-defined area of increased density, a poorly defined hazy region, or occasionally an area of reduced density sitting in front of the heart. In some cases, an enlarged heart or a heart positioned slightly to the left can mimic the appearance of a fat pad even when there isn’t a prominent one.
CT scans provide much more detail. Fat has a characteristic density on CT, falling between negative 200 and negative 30 Hounsfield units (the scale radiologists use to identify tissue types). This makes it straightforward to distinguish fat from fluid, tumors, or other structures. On ultrasound, pericardial fat appears as a somewhat uneven, echo-free space that moves in sync with the heartbeat. It doesn’t form a uniform ring around the heart. Instead, it clusters in certain areas, which is why it can sometimes be mistaken for a mass or a small fluid collection by less experienced readers.
Conditions That Can Look Similar
When a pericardial fat pad shows up prominently on imaging, radiologists need to rule out a few other possibilities. A Morgagni hernia, where abdominal fat or even loops of bowel push through a small opening in the front of the diaphragm, can look nearly identical to a large fat pad on a standard X-ray. CT scans with reformatted images can usually tell the difference by showing blood vessels from the abdomen passing through the defect. Pericardial cysts, which are fluid-filled sacs that develop near the heart, also occupy the same general area but have a different density on CT.
Normal Thickness by Age, Sex, and Weight
A study using CT scans to establish reference values found that pericardial fat pad thickness increases predictably with age. Adults between 18 and 35 averaged 4.2 mm, those between 36 and 50 averaged 5.1 mm, and those between 51 and 70 averaged 6.4 mm. Men had thicker fat pads on average (5.6 mm) compared to women (5.0 mm).
Body weight showed the strongest correlation. People weighing 45 to 60 kg (roughly 100 to 130 pounds) averaged 4.5 mm, while those weighing 106 to 120 kg (about 235 to 265 pounds) averaged 6.7 mm. These numbers give clinicians a baseline for comparison. A fat pad within these ranges for your age and weight is considered normal.
Why Pericardial Fat Matters for Heart Health
Having some fat around the heart is completely normal and may serve protective and metabolic functions. But when the amount of fat grows beyond typical levels, it becomes clinically relevant. Epicardial fat in particular is metabolically active, meaning it doesn’t just sit passively. It produces signaling molecules that can influence the heart muscle directly, thanks to that shared blood supply. Researchers describe it as a small endocrine organ sitting right on the heart’s surface. The fat outside the pericardium does not appear to have this same direct chemical relationship with the heart.
A large meta-analysis pooling data from over 73,000 patients found that higher pericardial fat volume was significantly associated with coronary artery disease, with a 38% increased odds of having the condition compared to people with less fat. The association with atrial fibrillation has also drawn attention, though data on other heart rhythm problems remains limited. Because pericardial fat correlates strongly with overall obesity, researchers have proposed incorporating fat pad measurements into cardiovascular risk assessments alongside traditional factors like blood pressure and cholesterol.
What Causes a Larger Fat Pad
The same factors that drive fat accumulation elsewhere in the body drive it around the heart. Higher body weight, older age, and male sex are the strongest predictors. Metabolic syndrome, which involves a cluster of conditions including high blood sugar, elevated triglycerides, and abdominal obesity, is closely linked to increased epicardial fat. The fat pad itself rarely causes symptoms. People don’t feel it, and it doesn’t typically interfere with the heart’s function unless it reaches extreme amounts or contributes to underlying coronary disease over time.
Weight loss reduces pericardial fat. Studies have shown that both lifestyle changes and weight-loss procedures lead to measurable decreases in epicardial fat thickness, though the clinical benefit of targeting this fat specifically, rather than reducing overall body fat, is still being worked out. For most people, a pericardial fat pad noted on imaging is simply a reflection of their overall body composition and not something that requires separate treatment.