A significant reduction in plasma free triiodothyronine (T3) (P less than 
0.0001) has been observed in patients undergoing open heart surgery. The 
beneficial effect of T3 would appear to be associated with increased synthesis 
and utilization of myocardial high energy stores. We have therefore administered 
T3 (4-10 micrograms iv) to 10 patients either when difficulty was being 
experienced in weaning from cardiopulmonary bypass (CPB) support (n = 5), or 
when myocardial function remained extremely poor (n = 5), despite inotropic and 
intraaortic balloon pump support. Mean preoperative NYHA functional class of the 
10 patients was 3.2, left ventricular enddiastolic pressure (LVEDP) 20 mm Hg and 
ejection fraction (EF) 40%. The mean myocardial ischaemia time was 72 min (range 
40-120 min). Within 1 h of T3 administration the mean plasma free T3 level had 
risen from 1.03 to 3.56 micrograms/ml and CPB was discontinued in all 5 cases. 
Balloon pump support (n = 2) was no longer essential within 3 h. At 1 h, the 
mean arterial pressure (MAP) had risen from 42 to 78 mm Hg, and heart rate (HR) 
from 90 to 104 beats/min; the left atrial pressure (LAP) had fallen from 30 to 
14 mm Hg, and the central venous pressure (CVP) from 20 to 11 cm H2O. (All 
changes significant at P less than 0.0001.) Inotropic support had been 
significantly reduced or discontinued. To our knowledge, T3 has not been 
administered previously as an inotropic agent to patients who have undergone 
cardiac surgery. We believe that T3 may have an important role in the rescue of 
failing hearts following a period of myocardial ischaemia in patients who have 
undergone open heart surgery.