A valvular heart disorder in which one or both mitral valve flaps close incompletely during systole usually producing either a click or murmur and sometimes minor mitral regurgitation and which is often a benign symptomless condition but may be marked by varied symptoms (as chest pain, fatigue, dizziness, dyspnea, or palpitations) leading in some cases to endocarditis or ventricular tachycardia--abbreviation MVP; called also Barlow's syndrome.