Mitral valve prolapse Myxomatous mitral valve degeneration UMLS:C0264885 SNOMEDCT_US:42069006 SNOMEDCT_US:253395003 HP:0004764 Myxomatous mitral valve is defined as the presence of excess leaflet tissue and leaflet thickening greater than 5 mm, resulting in a prolapse greater than 2 mm into the left atrium on parasternal long axis view.