fibrillation

noun

fi·​bril·​la·​tion ˌfi-brə-ˈlā-shən  ˌfī- 

1

: an act or process of forming fibers or fibrils

2

a

: a muscular twitching involving individual muscle fibers acting without coordination

b

: very rapid irregular contractions of the muscle fibers of the heart resulting in a lack of synchronism between heartbeat and pulse

Examples of fibrillation in a Sentence

Recent Examples on the Web

My heart has an irregular rhythm, a condition known as atrial fibrillation that requires me to take the blood thinner Eliquis. —Chicago Tribune, 18 Jan. 2026

Its electrophysiology products include devices used by electrophysiologists and interventional cardiologists for the treatment of cardiac arrythmias, such as atrial fibrillation. —Kenneth Squire, CNBC, 17 Jan. 2026

World-first findings on coffee and irregular heartbeat University of Adelaide and University of California, San Francisco (UCSF) researchers led a randomized clinical trial of 200 adults from Australia, the US and Canada with atrial fibrillation (AF) to test coffee's impact on irregular heartbeats. —New Atlas, 2 Jan. 2026

Untreated atrial fibrillation can lead to heart failure after a long period of time. —Angelica Stabile, FOXNews.com, 16 Dec. 2025

Word History

First Known Use

1845, in the meaning defined at sense 1

Rhymes for fibrillation

• abdication
• aberration
• abjuration
• abnegation
• abrogation
• acceptation
• acclamation
• acclimation
• accusation
• activation
• actuation
• acylation

Medical Definition

fibrillation

noun

fi·​bril·​la·​tion ˌfib-rə-ˈlā-shən  ˌfīb- 

1

: an act or process of forming fibers or fibrils

2

a

: a muscular twitching involving individual muscle fibers acting without coordination

b

: very rapid irregular contractions of the muscle fibers of the heart resulting in a lack of synchronism between heartbeat and pulse see atrial fibrillation, ventricular fibrillation