An extra heartbeat that occurs before the normal heartbeat is due, disrupting the regular rhythm of the heart.
From 'extra-' (beyond) + 'systole' (from Greek systole, meaning contraction). The term was coined in cardiology in the late 1800s to describe premature heart contractions.
Your heart has a drummer keeping the beat, but sometimes a second drummer hits their cymbal at the wrong time—that's an extrasystole, and it's why people sometimes feel their heart 'skip' even though it's just extra busy.
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