The simple idea
- Pericarditis — the bag is inflamed. It causes sharp chest pain that is worse lying flat and better sitting forward. Doctors may hear a scratchy rub. It is usually treated with anti‑inflammatory medicines and rest.
- Pericardial effusion — fluid collects in the bag. A little is often harmless.
- Tamponade — so much fluid, so fast, that the heart can't fill. Blood pressure falls, the neck veins rise, and the patient can go into shock. This is an emergency: the fluid must be drained with a needle.
- Constriction — the bag becomes stiff and scarred, like a tight shell, slowly stopping the heart from filling.