extrasystole

As nouns the difference between contraction and extrasystole

is that contraction is a reversible reduction in size while extrasystole is extrasystole.

As an adjective premature

is occurring before a state of readiness or maturity has arrived.

As a noun extrasystole is

a premature contraction of the heart, producing an interruption or irregularity in heartbeat rhythm, associated with heart disease or the use of some pharmaceuticals.

As nouns the difference between extrasystole and extrasystolia

is that extrasystole is extrasystole while extrasystolia is (medicine) an alteration in the rhythm of the heart due to extrasystoles.