Acute pericarditis is inflammation of the pericardium, the thin two-layered sac that surrounds and protects the heart. It causes sharp chest pain that often worsens when you breathe in or lie flat, and it improves when you lean forward. Over 80% of cases end up labeled “idiopathic,” meaning no specific cause is identified, though a viral infection was long assumed to be the trigger in most of those cases. Recent evidence has cast doubt on that assumption, and the true cause often remains unknown.
What the Pericardium Does
The pericardium has two layers: an outer fibrous layer (the parietal pericardium) and an inner layer made of a single sheet of cells (the visceral pericardium). Between these layers sits a small amount of fluid that reduces friction as the heart beats. The sac also acts as a barrier, preventing infections or inflammation from nearby organs from reaching the heart itself. When the pericardium becomes inflamed, these layers rub against each other, producing pain and sometimes an audible scratching sound.
Common Causes
In most cases, doctors never pin down a definitive cause. Various viruses have been associated with pericarditis in case reports, but a study examining infection rates during a national lockdown found that dramatic drops in circulating viruses (influenza A down 99%, respiratory syncytial virus down 98%, enterovirus down 82%) did not produce a corresponding drop in pericarditis cases. This suggests that labeling every unexplained case as “presumed viral” is probably inaccurate.
When a specific cause is identified, possibilities include autoimmune conditions like lupus or rheumatoid arthritis, kidney failure (where toxic metabolic byproducts irritate both pericardial layers), bacterial or fungal infections, heart surgery, chest trauma, and certain cancers. Some cases follow a heart attack, when inflammation spreads to the surrounding pericardium.
How It Feels
The hallmark symptom is sharp, stabbing chest pain, typically behind the breastbone or on the left side. The pain gets worse when you breathe deeply, swallow, cough, or lie down. Sitting up and leaning forward reliably takes some pressure off, which is why many people instinctively adopt that position. This postural pattern is one of the clearest clues that chest pain is coming from the pericardium rather than the heart muscle itself.
The pain can radiate to the neck, shoulders, or back, and it sometimes mimics a heart attack. Fever, fatigue, and a general sense of feeling unwell often accompany it. Because chest pain has many possible causes, getting evaluated quickly matters.
How It’s Diagnosed
A 2025 expert consensus from the American College of Cardiology lays out the current diagnostic approach. Pleuritic chest pain (or an equivalent presentation) must be present, plus at least one additional finding. Two or more additional findings make the diagnosis definitive. Those findings include:
- Pericardial friction rub: A high-pitched, scratchy sound heard through a stethoscope, best detected when you lean forward after breathing out. The classic rub has three components, corresponding to the heart’s contraction, rapid filling, and late filling phases. It shows up in fewer than one-third of cases, is often subtle, and can come and go.
- ECG changes: Present in up to 60% of cases. The electrocardiogram progresses through four stages: first, widespread ST-segment elevation and PR-segment depression; then normalization of those segments; followed by diffuse T-wave inversions; and finally a return to normal. Unlike a heart attack, which produces localized changes, pericarditis tends to affect leads across the entire tracing.
- Elevated inflammatory markers: Blood tests showing a rise in C-reactive protein (CRP) or sedimentation rate confirm that inflammation is active. CRP is also used to track recovery and guide how long treatment should continue.
An echocardiogram (ultrasound of the heart) is typically performed to check for fluid buildup around the heart, which can develop as a complication.
Treatment
The standard first-line approach combines two medications. A full-dose anti-inflammatory drug, usually high-dose aspirin or ibuprofen, is taken for at least 7 to 14 days. The full dose continues until CRP levels return to normal, then the medication is gradually tapered over an additional one to two weeks to prevent the inflammation from bouncing back.
Colchicine, a plant-derived anti-inflammatory, is added from the start. It is dosed by weight: 0.5 mg once daily for people under 70 kg (about 154 lbs), or 0.5 mg twice daily for those above that weight. No loading dose is needed. For a first episode, colchicine is continued for three months. If pericarditis recurs, the course extends to six months. Colchicine has been shown to significantly reduce the chance of recurrence, which is why it’s now considered essential rather than optional.
Physical activity restriction is part of treatment. Current guidelines recommend at least one to three months away from vigorous exercise, though a minimum of two to four weeks of rest is generally useful to see whether symptoms are resolving. Return to activity should be gradual. For competitive athletes, exercise stress testing and heart rhythm monitoring may be recommended before returning to high-intensity training, especially if there’s any concern that inflammation extended into the heart muscle itself.
Complications to Watch For
The most serious near-term complication is cardiac tamponade, which occurs when fluid accumulates rapidly around the heart and compresses it, preventing it from filling properly. The first sign is often a fast heart rate as the body tries to compensate for reduced blood output. The classic warning signs, known as Beck’s triad, are low blood pressure, visibly distended neck veins, and muffled or distant-sounding heartbeats. Another telltale sign is pulsus paradoxus, where systolic blood pressure drops by more than 10 mmHg when you breathe in. Tamponade is a medical emergency requiring drainage of the fluid.
Most cases of acute pericarditis, however, do not progress to tamponade and resolve fully with appropriate treatment.
Recurrence Risk
Roughly 30% of people who have a first episode of acute pericarditis experience a recurrence within 18 months. About 15% go on to have multiple recurrences. Recurrences typically produce the same symptoms as the initial episode and are managed with the same combination of anti-inflammatory medication and colchicine, though the colchicine course is extended to six months. Tapering medications too quickly is one of the most common triggers for recurrence, which is why the gradual step-down guided by CRP levels is so important. People who do experience repeated flares can generally still achieve long-term remission, but the treatment timeline stretches out with each recurrence.