1) Premature beat 2) Premature contraction 1) Systole 
a premature contraction of the heart that is independent of the normal rhythm and arises in response to an impulse in some part of the heart other than the sinoatrial node; called also premature beat.
A premature contraction of the heart that is independent of the normal rhythm and arises in response to an impulse in some part of the heart other than the sinoatrial node. ... Synonym: premature beat. ... (18 Nov 1997) ... 
(eks″trә-sis´to-le) a premature cardiac contraction that is independent of the normal rhythm and arises in response to an impulse outside the sinoatrial node.
Type: Term Pronunciation: eks′tră-sis′tō-lē Definitions: 1. A nonspecific word for an ectopic beat from any source in the heart. Synonyms: premature beat, premature systole
Extrasystole: A premature contraction of the heart that is independent of the normal rhythm of the heart and that arises in response to an impulse in some part of the heart other than the normal impulse from the sinoatrial (SA) node. The extrasystole is followed by a pause, as the heart electrical system 'resets' itself and the contraction followin...
noun a premature systole resulting in a momentary cardiac arrhythmia
a premature contraction of the heart, resulting in momentary interruption of the normal heartbeat. Also called