arrhythmia
n. any variation from the normal rhythm of the heartbeat. Kinds of arrhythmia include tachycardia, a rate above 100 beats per minute; bradycardia, a rate of less than 60 beats per minute; premature beats; atrial flutter, in which an upper chamber contracts up to 400 times per minute; and heart block, in which the heart fails to contract because of the interruption or delay of an electrical stimulus needed to trigger the contraction. —arrhythmic
adj.