Incidence and Etiology Congenital deformities of the mitral valve are rare if those involving the left valve in hearts with common atrioventricular junction are excluded Congenital mitral incompetence is even rarer The prevalence of congenital mitral or tricuspid valve disease was of 0.04 per 1000 children in a general population study.31 Most male-to-female ratios from recent surgical series of mitral valve repair or replacement vary from 0.74 to 0.89.32–35 Congenital mitral valvar anomalies are rarely isolated The fully developed syndrome of the so-called Shone complex,9 for example, includes four obstructions within the left heart, namely the valvar lesion itself, supravalvar mitral ring, subaortic stenosis, and aortic coarctation Any of these obstructions may coexist with any congenital lesion affecting the mitral valve, particularly coarctation In a clinical series of patients with congenital mitral stenosis and excluding hypoplasia of the left heart, almost three-quarters had additional anomalies.36 It is tempting to imagine that the development of one abnormality upstream may, during morphogenesis, result in a series of more distal abnormalities owing to disturbance in the patterns of flow Annular hypoplasia of the mitral valve is almost always associated with hypoplasia of the left ventricle and aortic stenosis or atresia VSD is quite common in this setting, and double-outlet right ventricle and tetralogy of Fallot occasionally occur When the mitral valve is imperforate, left ventricular hypoplasia is inevitable unless there is an associated VSD.9 Pathophysiology The pathophysiology is very closely linked to the age of the patient and the presence or absence of associated lesions that will allow the heart to maintain systemic output and to offload the pulmonary circulation Mitral stenosis or regurgitation results in elevation of the left atrial pressure Coexistence of an atrial septal defect decompresses the left atrium due to the left-to-right shunt favored by a better right ventricular compliance, as in partial atrioventricular septal defect with left atrioventricular valve regurgitation and primum atrial septal defect (see Chapter 29) This may be so profound as to obscure or eliminate the mitral gradient By contrast, excessive flow through the mitral valve, as may result from an associated VSD, will exaggerate the mitral gradient Elevation of the left atrial pressure usually results in pulmonary hypertension In the presence of associated patency of the arterial duct or a VSD, this can result in right-to-left shunting, which will be how the individual maintains systemic output in the neonatal period, whereas in the septated heart, the pulmonary arterial systolic pressure may exceed systemic pressure Later in life, the rise in pulmonary vascular resistance and consequent fall in pulmonary blood flow will generate a fall in the gradient; right heart failure may ensue By contrast, severe pulmonary stenosis in the setting of a VSD may entirely mask the effects of the valvar obstruction by reducing the flow of blood to the lungs In fully septated hearts, when moderate-to-severe mitral regurgitation is left to evolve during childhood, the systemic output is usually maintained until the end of the first decade, with preservation of the systolic function despite a considerable regurgitation fraction This adaptation occurs via extensive dialation of the left atrium and an increase of the left ventricular end-diastolic diameter There is hardly any left atrial or pulmonary hypertension Patients with chronic isolated mitral valve stenosis become symptomatic when the pulmonary vascular resistances increase (acutely during viral illnesses) or when the evolution of the interventricular interrelation modifies the diastolic function of the left ventricle Associated obstructive lesions downstream obviously increase the severity of the mitral regurgitation Clinical Presentation and Symptomatology Congenital disease of the mitral valve usually presents as a result of the associated abnormalities, such as coarctation or VSD In these lesions, the symptoms are exacerbated by the presence of the mitral valvar condition, but this may be too subtle to detect The effects of the valvar anomaly may be attenuated by lesions upstream to the mitral valve The result, whatever the associated anomaly, tends to be that mitral disease is masked and will not be recognized unless specially looked for or only after the correction of the associated defects The presentation of isolated mitral valvar disease is largely determined by the level of the left atrial and pulmonary artery pressure If this is close to normal, there are usually no symptoms At most, there will be fatigue after severe exertion A high left atrial pressure is likely to result in poor feeding, sweating in infancy, and failure to thrive Patients with severe obstruction are likely to present in intractable cardiac failure in the first month or so of life Orthopnea is extremely rare, but patients frequently complain of a dry nocturnal cough Wheezing and respiratory infections are frequent Syncope, hemoptysis, or aphonia―owing to compression of the recurrent laryngeal nerve by an enlarged left atrium―have occasionally been described Pure mitral stenosis is characterised by poor nourishment, tachypnea, and intercostal recession There are normal to small peripheral arterial pulses, and the jugular venous pulse is also usually normal If pulmonary hypertension is severe, a prominent a wave will reflect the raised right ventricular end-diastolic pressure A systolic wave will demonstrate secondary tricuspid incompetence Palpation of the heart will reveal either a normal impulse or right ventricular hypertrophy, and there may be an apical diastolic thrill Pulmonary valvar closure will be palpable if pulmonary hypertension is severe The first heart sound is either normal or loud and, in contrast to rheumatic mitral stenosis, an opening snap is only occasionally audible Closure of the pulmonary valve is accentuated in patients with pulmonary hypertension There is a loud low-pitched mid-diastolic murmur at the apex, usually with presystolic accentuation Occasionally no diastolic murmur is heard In severe untreated disease, an early diastolic murmur of pulmonary incompetence and a pansystolic murmur of tricuspid incompetence may be heard, both resulting from pulmonary hypertension Crepitations may be