Most patients with advanced congestive heart failure have altered thyroid 
hormone metabolism. A low triiodothyronine level is associated with impaired 
hemodynamics and is an independent predictor of poor survival. This study sought 
to evaluate safety and hemodynamic effects of short-term intravenous 
administration of triiodothyronine in patients with advanced heart failure. An 
intravenous bolus dose of triiodothyronine, with or without a 6- to 12-hour 
infusion (cumulative dose 0. 1 5 to 2.7 microg/kg), was administered to 23 
patients with advanced heart failure (mean left ventricular ejection fraction 
0.22 +/- 0.01). Cardiac rhythm and hemodynamic status were monitored for 12 
hours, and basal metabolic rate by indirect calorimetry, echocardiographic 
parameters of systolic function and valvular regurgitation, thyroid hormone, and 
catecholamine levels were measured at baseline and at 4 to 6 hours. 
Triiodothyronine was well tolerated without episodes of ischemia or clinical 
arrhythmia. There was no significant change in heart rate or metabolic rate and 
there was minimal increase in core temperature. Cardiac output increased with a 
reduction in systemic vascular resistance in patients receiving the largest 
dose, consistent with a peripheral vasodilatory effect. Acute intravenous 
administration of triiodothyronine is well tolerated in patients with advanced 
heart failure, establishing the basis for further investigation into the safety 
and potential hemodynamic benefits of longer infusions, combined infusion with 
inotropic agents, oral triiodothyronine replacement therapy, and new 
triiodothyronine analogs.