/ Dictionary / Index M mitral insufficiency: Meaning and Definition of Find definitions for: mi'tral insuffi'ciency Pronunciation: [key] abnormal closure of the mitral valve resulting in regurgitation of blood into the atrium and leading to reduced heart function or heart failure. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mitral mitral stenosis Related Content Daily Word Quiz: fervor Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language