noun
also ar·ryth·mia āˈrithmēə, aˈr- also -th-
( -s )
Etymology: New Latin, from Greek, lack of rhythm, from arrhythmos unrhythmical (from a- a- (II) + rhythmos rhythm) + -ia — more at rhythm
: an alteration in the rhythm of the heartbeat either in time or force that is of functional or organic origin — compare bradycardia , tachycardia ; fibrillation