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

Other types included in the new report are heart failure, when the heart struggles to fill with and pump blood; atrial fibrillation, a type of abnormal heart rhythm; and stroke. —Barbara Mantel, NBC news, 25 Feb. 2026

And the rates of numerous cardiovascular conditions, such as coronary disease, heart failure, stroke and atrial fibrillation could all rise slightly, according to the study. —Lauren J. Young, Scientific American, 25 Feb. 2026

Patients whose results read high on one platform may be started on thyroid hormone unnecessarily, risking overtreatment complications that include atrial fibrillation and bone loss. —Samantha Bonsack, STAT, 18 Feb. 2026

The certificate listed atrial fibrillation and pulmonary hypertension as contributing conditions. —Jami Ganz, Mercury News, 6 Feb. 2026

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