© 2013 Springer Science+Business Media New York. All rights reserved. Patients with various acute and chronic diseases have been documented to have a syndrome known as the euthyroid sick syndrome, the common factor in which would appear to be an increased output of circulating catecholamines associated with a generalized inflammatory response. These patients show a decrease in free T3 and an increase in reverse T3. A significant reduction in free T3 has also been documented in patients undergoing open-heart surgical procedures. Experimental data indicated that it was beneficial to the hemodynamic status of an animal or patient to receive treatment with T3 at the end of a period of cardiopulmonary bypass. This led to replenishment of myocardial energy stores and recovery of normal hemodynamic function more rapidly than if T3 was not administered. In view of the low levels of T3 observed in brain-dead potential organ donors and in patients undergoing heart transplantation on cardiopulmonary bypass, it is suggested that both donor and recipient should receive hormonal replacement therapy. Data suggest that T3 treatment to both heart donor and recipient is beneficial to outcome and is not associated with adverse side effects.