f wave

n.

A pattern of irregular undulations of the base line in an electrocardiogram that is indicative of atrial fibrillation.

F wave

n.

A pattern of regular, rapid atrial waves in an electrocardiogram, indicative of atrial flutter.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.