Pericarditis

The Heart's Squeezed Sleeping Bag

Imagine your heart is a fist pumping inside a sleeping bag (the pericardium). Normally, there's just enough slippery fabric between your fist and the bag so you can punch smoothly without friction — that's the tiny 15-50 mL of pericardial fluid acting like oil. Now suppose the sleeping bag lining gets irritated (inflamed by a virus or immune attack) and starts leaking water inside — the fabric gets sticky and swollen, your punches rub and hurt with every movement, and the bag fills with fluid. If the bag fills fast enough, the pressure inside rises so much that your fist can't expand fully on each squeeze, so less blood (like less movement of your fist) gets pushed out into the body — that's tamponade. Finally, if the bag never heals and scars into a stiff shell, your fist is choked even when empty — that's constrictive pericarditis, the chronic damage.