. We report three cases of transient myocardial hypertrophy, diagnosed by echocardiography, occurring between the second and seventh days of life in neonates with initially normal ventricular myocardial wall thickness. The three term neonates had perinatal injury with acute fetal distress. In all three cases electrocardiographic and biologic signs of myocardial ischemia were present. The first echocardiographic results showed abnormalities in systolic or diastolic left ventricular function, without hypertrophy of the walls. The hypertrophic cardiomyopathy (HCM) occurred between days 2 and 7 and affected first the interventricular septum and the free wall of the right ventricle. The left ventricular posterior wall subsequently became abnormal, resulting in severe overall myocardial hypertrophy, which finally disappeared in all three cases between 1 and 5 months of life. Such observations of early severe and transient HCM have not been previously reported. We believe it is a consequence of myocardial ischemia due to acute fetal distress. The prognosis of this type of HCM is good, in contrast to that of other primitive HCM occurring in neonates.