extrasystole
ex·tra·sys·to·le
noun \-ˈsis-tə-(ˌ)lē\Definition of EXTRASYSTOLE
: a prematurely occurring beat of one of the chambers of the heart that leads to momentary arrhythmia but leaves the fundamental rhythm unchanged—called also premature beat
—ex·tra·sys·tol·ic \-sis-ˈtäl-ik\ (audio pronunciation) adjective
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