Summary Heart failure in the newborn infant is characterized by tachypnea, tachycardia, feeding difficulties, pulmonary râles and rhonchi, hepatic enlargement, and cardiomegaly. Less common signs include visibly elevated systemic venous pressure, peripheral edema, ascites, pulsus alternans, gallop rhythm, and inappropriate sweating. When heart failure occurs in the first days and weeks of life it is usually due to structural congenital heart disease or to primary myocardial disease. It may on occasion, however, be secondary to arrhythmia, respiratory disease, central nervous system disease, anemia, systemic or pulmonary hypertension, or septicemia. The distinction between left heart failure and right heart failure is less obvious in the newborn infant than in the older child or adult. The newborn infant with advanced near-terminal heart failure is often pallid and apathetic. He has minimal spontaneous movements, diminished peripheral pulses, bradycardia, apneic periods, splenic enlargement, widespread peripheral edema, and gross cardiomegaly. Near-terminal heart failure may closely simulate septicemia, meningitis, bronchiolitis, or severe pneumonia. Certain noncardiac conditions may also simulate heart failure. Such conditions include hypoglycemia, many forms of respiratory disease, renal disease, the rubella syndrome, liver enlargement due to a variety of diseases, factitious cardiomegaly, cardiomegaly not due to heart failure, peripheral edema due to hypoalbuminemic states or lymphedema, and ascites due to escape of chyle or liver disease. The management of heart failure in the newborn infant requires a rapid assessment of the effect of the medical measures described. Deterioration or failure to improve within 12 hours is usually an indication for cardiac catheterization and angiocardiography. In general, the younger the infant the more urgent are diagnostic studies and surgery, if indicated. The use of an incubator is essential for optimal care. A number of emergency measures are available for the critically sick newborn infant with heart failure. The usual objective of these more drastic measures is to produce a temporary improvement so that other measures which may provide longer range benefit may be utilized.