My son started them at 5 yrs old as hopefuly a means of slowing down cardiomiopathy. He was started on Enalapril. He is now on Losartan - 50mg/day. He has no problems with his heart as of yet. No side effects from the meds.
Justin started a heart medication the day we tested his heart shortly after we were aware of his DMD status. His injection fraction (I think it is called) was at the lower limit and after a few months of the medication it was at the upper limit and remains there, it is nearly 3 years ago now. He is checked for heart function every 6 months now.
He has a daily dose of Tri Tace 2.5mg along with Steroids, Calcium & Vitamin D.