The thin, smooth innermost layer of the heart that lines all four chambers and covers the heart valves, allowing blood to flow without clotting.
From Greek 'endo-' (within) + 'kardia' (heart) + Latin '-ium' (denoting tissue). Anatomists named this layer in the 19th century as microscopic examination revealed the heart's layered structure.
Your endocardium has to be perfectly smooth like the inside of a brand-new pipe—any roughness from infection or damage causes blood to stick and clot, which is why endocarditis is so dangerous.
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