Isolated noncompaction of the left ventricular myocardium is a rare cardiomyopathy typically showing a "spongy" myocardium on ultrasound. We report on the ultrasonic and pathomorphological characteristics of an infant who, at the age of 40 days, was treated by heart transplantation for isolated noncompaction. Noncompaction should be suspected in newborns with otherwise unexplained cardiomyopathy and a "spongy" left ventricle. However, ultrasonic and pathological findings may be much less pronounced at this age than later in life.