Congestive heart failure in the first weeks of life is frequently caused by coarctation of the aorta, which may be diagnosed by clinical examination. The femoral pulsations are weak or absent with the blood pressure in the arms being considerably higher than in the legs. If the left subclavian artery originates below the level of the coarctation the pressure in the left arm is also low. The electrocardiograms of these infants are compatible with right ventricular hypertrophy or dilatation. The chest X-ray reveals marked cardiomegaly. This corresponds with the severely dilated right ventricle seen by echocardiography. The circulation of blood through the lower part of the body, and thus the kidneys, is reduced, which results in water and salt retention. The left ventricle often has thick walls with a diminished compliance and is frequently slightly smaller than normal. Thus, the fluid retention more readily dilates the right than the left ventricle. The aorta is usually slender and the aortic valve almost always bicuspid (chapter 10). A concomitant mitral lesion, not infrequently seen with coarctation of the aorta (1), e.g. parachute mitral valve, demands careful two-dimensional echocardiographic analysis of the mitral region.