Relating to or affecting the atria, especially the upper chambers of the heart.
From Latin atrium with -al adjectival suffix, meaning 'of or relating to the atrium.' Became standard in cardiac medicine terminology during the 19th century.
Atrial fibrillation, a common heart rhythm problem, happens when the atria quiver instead of beating strongly—it's like your heart's lobby is shaking instead of pushing blood through smoothly.
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