congenital mitral valve insufficiency and/or stenosis congenital accessory mitral valve tissue https://www.malacards.org/card/accessory_mitral_valve_tissue MEDGEN:576493 Orphanet:99061 GARD:0019628 UMLS:C0344774 MONDO:0020402 Accessory mitral valve tissue is a congenital non-syndromic heart malformation defined as an accessory mitral valve leaflet or various accessory mitral valve structures. It may be asymptomatic or present at various ages with symptoms of left ventricular outflow tract obstruction, low cardiac output due to subaortic obstruction or congestive heart failure. In some cases, it may be a source of cardioembolism. The malformation may be isolated or associated with other congenital heart malformations.