Neonatal thyrotoxicosis may occur by transplacental transfer of thyroid stimulating immunoglobins from the mother. Although the clinical manifestations may vary in the new-born period, hyperthyroidism has been associated with several cardiac complications including supraventricular tachycardia, cardiomyopathy and congestive cardiac failure. We report the case of a nine day old baby who presented with severe pulmonary hypertension in association with congestive cardiac failure secondary to neonatal thyrotoxicosis. Treatment of the heart failure and restoration of the thyroid function resulted in complete regression of the pulmonary hypertension. The recognition and reversibility of pulmonary hypertension in neonatal Graves disease has not been previously described.