Two patients with congenital mitral incompetence and coarctation of the aorta are presented. One patient had associated patent ductus arteriosus, bicuspid aortic valve, and endocardial fibroelastosis. The diagnosis in the two patients presented is well established by clinical, laboratory, and surgical findings and also by necropsy examination in one case. It is proposed that the rarity of reported cases in the literature may have resulted from the frequent diagnosis of left ventricular failure in infancy secondary to coarctation, leading to the assumption that a mitral insufficiency murmur, when present, is due to functional regurgitation. Likewise, the murmur may be mistakenly thought to originate from a ventricular septal defect.The diagnosis of coarctation of the aorta presented no problem in either patient, while detection of the mitral incompetence was difficult. Coarctation of the aorta complicated by pulmonary hypertension in the absence of intracardiac shunt should draw attention to the possibility of associated mitral incompetence. Congestive heart failure, especially after correction of coarctation, was also an indication of possible associated mitral insufficiency.The two patients were treated by repair of coarctation of the aorta at 3 months and 3 years of age and by mitral valve replacement at the age of 18 months and 5 years, respectively. One patient was in terminal heart failure and died following mitral valve surgery. The other patient benefited from the operation and her case has been followed for over one year. Correction of coarctation of the aorta provided only temporary relief of heart failure. Until both anomalies are corrected response will generally be unsatisfactory.The aetiology of combined mitral incompetence and coarctation of the aorta can be explained on a congenital basis. Endocardial fibroelastosis of the left ventricle is thought to be secondary to coarctation of the aorta, mitral incompetence, or both.