Patients with intraatrial baffle procedure for transposition of the great 
arteries (TGA) have diastolic dysfunction, decreased exercise capacity, stroke 
volume response and elevated systemic vascular resistance (SVR) during exercise. 
Angiotensin-converting enzyme (ACE) inhibitors improve exercise capacity in 
adults with congestive heart failure by improving diastolic function and 
decreasing SVR. We tested the hypothesis that ACE inhibitors decrease SVR and 
improve exercise capacity in patients after intraatrial baffle procedure for 
TGA. We studied the effects of enalapril in nine patients with TGA s/p 
intraatrial switch (mean age, 13.8 +/- 3 years) 7 to 21 years (mean, 12 +/- 4 
years) after intraatrial baffle procedure. Enalapril (0.5 mg/kg/day, maximum 
dosage 20 mg bid) was administered for 12 months. Patients exercised using a 
cycle ergometer ramp protocol (0.25 W/kg/min) before enalapril (baseline), 1 
month, 6 months, and 12 months after treatment initiation. Heart rate, blood 
pressure, cardiac output, respiratory rate, minute ventilation, oxygen 
consumption (VO2), total exercise time, work, and power were measured. SVR, 
cardiac index, and stroke volume index (SVI) were calculated. Two-tailed paired 
Student's t-test was used to compare data to those of normal control patients 
and the patients' baseline data. Patients had lower resting heart rate, cardiac 
index, maximum heart rate, cardiac index (CI), SVI, VO2, exercise time, work, 
and power and higher maximal SVR at baseline compared to normal control 
patients. There was no significant difference in total exercise time, work, 
power, VO2 (rest/peak), SVR, SVI, and CI after 12 months of therapy compared to 
patients' baseline values. We conclude that short-term (<1 year) use of 
enalapril does not improve exercise performance in patients with TGA in whom the 
intraatrial baffle procedure has been performed.