Question: In what proportion of children with heart failure has Enalapril been shown to be safe and effective?

Context:
The responses to IV KCl were attenuated by concomitant furosemide (p = 0.01), amphotericin B (p < 0.01), and KCl in parenteral nutrition (p < 0.01). The responses were augmented by concomitant enalapril
To determine whether an angiotensin-converting enzyme (ACE) inhibitor, enalapril, prevents cardiac function deterioration (defined using maximal cardiac index [MCI] on exercise testing or increase in left ventricular end-systolic wall stress [LVESWS]) in long-term survivors of pediatric cancer.
Enalapril treatment did not influence exercise performance, but did reduce LVESWS in the first year
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.
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.
A common late effect of doxorubicin therapy for childhood cancer is reduced left-ventricular (LV) wall thickness resulting in elevated LV afterload and depressed LV function. Many children are given angiotensin-converting enzyme inhibitors, which have been studied primarily in adults. We document the long-term effects of angiotensin-converting enzyme inhibitors in doxorubicin-treated survivors of childhood cancer.
In doxorubicin-treated long-term survivors of childhood cancer, enalapril-induced improvement in LV structure and function is transient. The primary defect, which is LV wall thinning, continues to deteriorate, and thus the short-term improvement was mostly related to lowered diastolic blood pressure.
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.
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.
Angiotensin convertase inhibitor (Enalapril) was used in 51 children aged 4 days up to 18 years (mean 4.3 +/- 5.5, years). As many as 27 subjects were newborns (4) and infants (23). The patients suffered from circulatory insufficiency due to congestive cardiomyopathy (13 cases). 6 treated subjects suffered from circulatory insufficiency due to congenital heart malformations before cardiac surgery and 22 after it (including complex malformations operated according to Fontan method). 10 children were treated because of arterial hypertension. 4 subjects suffered form life-threatening arrhythmias coexisting with circulatory insufficiency.
4 patients (8%) died during treatment but their deaths can not be related to angiotensin convertase inhibitor therapy. In the other children (82%) the beneficial influence of angiotensin convertase inhibitor use was found (improvement in comparison with the state before convertase inhibitor introduction). In 10% of subjects enalapril did not show any significant therapeutic effect
We conclude that the combination of ACE inhibitor and beta-blocker deserves further exploration for inclusion in any management regimen for the treatment of muscular dystrophy-associated cardiomyopathy.
Addition of these medications, never before attempted in the management of cardiomyopathy associated with generalized myopathic disease, complemented each other in relieving symptoms and reversing signs of congestive heart failure and DCM.
Enalapril was clinically safe and effective for children with cardiac failure secondary to ventricular impairment, valvar regurgitation, or after cardiac surgery. Renal failure was a problem in young infants with left-to-right shunts.
In a tertiary referral centre 63 patients underwent 67 treatment periods with enalapril. The median age was 5.4 months. All children had signs of heart failure: congestive cardiac failure with breathlessness at rest was present in 88%. Haemodynamic groups were left-to-right shunt (n = 15), impaired ventricular function (n = 14), after cardiac surgery (n = 23), valvar regurgitation (n = 12), and hypertension (n = 3). Serial clinical, radiological, and laboratory data were used to judge outcome. The mean (SD) maximal dose was 0.30 (0.21) mg/kg/day. Thirty nine (58%) patients improved, 20 (30%) showed no improvement, and eight (12%) had side effects requiring discontinuation of enalapril.
We studied the inhibition of angiotensin converting enzyme (ACE) in eight infants with congestive heart failure (CHF) poorly controlled with digoxin and diuretics, treated orally with 0.25 mg kg-1 enalapril maleate once a day
In infants with CHF, mean baseline ACE activity was significantly higher than in control infants
Converting enzyme inhibitors may benefit "heart failure" associated with large ventricular septal defects and normal or mildly elevated pulmonary resistance.

Answer: In children with heart failure evidence of the effect of enalapril is empirical. Enalapril was clinically safe and effective in 50% to 80% of for children with cardiac failure secondary to congenital heart malformations before and after cardiac surgery,  impaired ventricular function , valvar regurgitation,  congestive cardiomyopathy,  , arterial hypertension, life-threatening arrhythmias coexisting with circulatory insufficiency.   
ACE inhibitors have shown a transient beneficial effect on heart failure due to anticancer drugs and possibly a beneficial effect in muscular dystrophy-associated cardiomyopathy, which deserves further studies.
Exact answer: 50% to 80%