ECG observations in patients critically ill from various CNS problems suggest that T wave abnormalities in these patients may be neurogenic rather than the result of cardiac ischemia. This phenomenon has been experimentally reproduced in the cat. Right hypothalamic stimulation in this species markedly increases T wave amplitude while left hypothalamic stimulation decreases T wave amplitude. ECG results similar to those following right hypothalamic stimulation were obtained by stimulation of the right stellate ganglion and this was also true with regard to left hypothalamic and left stellate ganglion stimulation. ECG effects of unilateral hypothalamic stimulation could be abolished by removal of the ipsilateral stellate ganglion. These results demonstrate that T wave changes on the ECG may be neurogenic and suggest that the mechanism for their production is a unilateral alteration of sympathetic tone to the heart.