BACKGROUND: Angiotensin-converting enzyme inhibitors improve exercise capacity 
in adults with congestive heart failure by decreasing systemic vascular 
resistance and improving ventricular diastolic function. Patients who have 
undergone the Fontan procedure have decreased cardiac output, increased systemic 
vascular resistance, abnormal diastolic function, and decreased exercise 
capacity compared with normal people.
METHODS AND RESULTS: To test the hypothesis that afterload reduction therapy 
alters hemodynamic variables and augments exercise capacity in patients after a 
Fontan procedure, we compared the results of graded exercise with maximal effort 
from 18 subjects (14.5+/-6.2 years of age, 4 to 19 years after Fontan procedure) 
in a randomized, double-blind, placebo-controlled crossover trial using 
enalapril (0.2 to 0.3 mg x kg[-1] x d[-1], maximum 15 mg). Each treatment was 
administered for 10 weeks. Diastolic filling patterns at rest were assessed by 
Doppler determination of the systemic atrioventricular valve flow velocity at 
the conclusion of each therapy. No difference was detected in resting heart 
rate, blood pressure, or cardiac index. Diastolic filling patterns were also 
similar. Exercise duration was not different (6.4+/-2.6 [enalapril] versus 
6.7+/-2.6 minutes [placebo]). The mean percent increase in cardiac index from 
rest to maximum exercise was slightly but significantly decreased in subjects 
after 10 weeks of enalapril therapy (102+/-34% [enalapril] versus 125+/-34% 
[placebo]; P<.02). At maximal exercise, cardiac index (3.5+/-0.9 [enalapril] 
versus 3.8+/-0.9 L x min[-1] x m2 [placebo]), oxygen consumption (18.3+/-9 
[enalapril] versus 20.5+/-7 mL x min[-1] x kg[-1] [placebo]), minute ventilation 
(57.5+/-17 [enalapril] versus 55.4+/-19 L/min [placebo]), and total work 
(247+/-181 [enalapril] versus 261+/-197 W [placebo]) were not different.
CONCLUSIONS: We conclude that enalapril administration for 10 weeks does not 
alter abnormal systemic vascular resistance, resting cardiac index, diastolic 
function, or exercise capacity in patients who have undergone a Fontan 
procedure.