On admission, he was a well-appearing boy. His height was 113 cm, 25th percentile; weight, 19.5 kg, 50th percentile. He had no dysmorphic features and resembled other family members. Remarkable findings included a 2/6 systolic ejection murmur maximal at the upper left sternal border that transmitted along the left sternal border as well as to the back on the left. S1 and S2 were normal; diastole, quiet; pulses, full and equal. Occasional premature beats were noted during auscultation. He was alert and responded to questions appropriately. Results of cranial nerve, motor, cerebellar, sensory, and deep tendon reflex tests were normal. A chest x-ray film showed a generous heart size with slight left ventricular prominence. Lung fields were clear. Electrocardiography showed sinus rhythm with frequent premature atrial contractions but no premature ventricular contractions. The QT interval was slightly prolonged at 0.45 seconds. The QRS axis was+130 with large Q waves over the right precordium and no Q waves over the left. Echocardiography (Figure 1) demonstrated a globular heart with left ventricular trabeculation. Shortening fraction was 28%. Hemodynamically insignificant mild pulmonary stenosis, pulmonary insufficiency, tricuspid regurgitation, and aortic insufficiency were also noted. Exercise study results were uneventful. Holter monitoring showed frequent premature atrial contractions but no evidence of supraventricular tachycardia. There were 2 premature ventricular contractions during the 24-hour monitoring. Results of an electroencephalogram were normal.