A complete absence of heart activity and electrical activity, meaning the heart has stopped beating entirely; cardiac standstill.
From Greek 'a-' (without) + 'systole' (contraction of the heart). 'Systole' comes from Greek 'systolé' meaning 'contraction,' so asystole literally means 'without contraction.'
In medical emergencies, asystole is the scariest rhythm doctors can see on heart monitors because it looks like a flat line—and despite what TV shows suggest, shocking a flatline with a defibrillator doesn't usually work, which is why real CPR is so critical.
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