The appointment goes well. The echocardiogram looks normal, the ECG looks normal, the ejection fraction is where it should be. Then the cardiologist says it's time to start your son on a daily heart medication, and the room reorganizes itself around that sentence. Nothing on the screen suggested his heart was in trouble. So why treat it?

The answer is that the tests are not measuring what the medication is protecting.

An Ejection Fraction Is a Rearview Mirror

Ejection fraction describes the percentage of blood the left ventricle pushes out with each beat. It is a performance number, and the heart is very good at holding its performance steady while the muscle behind it changes. In Duchenne muscular dystrophy, the same missing dystrophin protein that damages skeletal muscle also damages cardiac muscle. Damaged cardiac cells are gradually replaced by scar tissue, a process called fibrosis, and healthy neighboring cells compensate by working harder.

That compensation is why the numbers stay normal. By the time ejection fraction slips below the normal range, a meaningful portion of the left ventricle has already been replaced by tissue that does not contract and never will. Scar tissue is permanent. There is no medication, in DMD or anywhere else, that converts fibrosis back into working muscle.

Cardiac MRI makes this visible. Using a contrast agent that concentrates in scarred tissue, MRI can show patches of fibrosis in the left ventricular wall years before ejection fraction drops on an echocardiogram. Boys with completely normal echo results have shown measurable scarring on MRI.

The medication, then, is aimed not at the damage an echo would eventually catch but at the muscle that is still healthy when the prescription is written.

What the Evidence Showed

The standard first medication is an ACE inhibitor, a class that includes lisinopril, enalapril, and perindopril. These drugs relax blood vessels, which lowers the pressure the left ventricle has to pump against. Less resistance means less mechanical strain on each cell, and cells under less strain break down more slowly. When a persistent dry cough makes an ACE inhibitor hard to tolerate, an ARB such as losartan does similar work through a different receptor.

The reason cardiologists put a number on it comes from a French trial that enrolled 57 boys with DMD between roughly ages nine and thirteen, all with normal left ventricular function at the start. Half received perindopril and half received placebo for three years, after which everyone was offered the medication. The early-treatment group entered the open phase with heart function that had held steadier. Ten years after enrollment, about 93 percent of the boys who started early were alive, compared with about 66 percent of those whose treatment began three years later.

That is a small trial, and a single one. It is also the clearest available comparison between starting before dysfunction and starting after, and the size of the gap is what moved the field. The 2018 international DMD care considerations, the document most pediatric cardiology teams work from, recommend beginning an ACE inhibitor or ARB by age 10 regardless of what imaging shows. Some teams start earlier, particularly when cardiac MRI has already found fibrosis.

Other medications enter later or in combination. Beta blockers reduce heart rate and contraction force, lowering the heart's oxygen demand. Eplerenone, which blocks a hormone that drives cardiac scarring, slowed the decline of heart muscle strain in a trial of boys who already had fibrosis but still had preserved ejection fraction. Corticosteroids prescribed for skeletal muscle appear to delay cardiac involvement as a secondary benefit.

The First Few Weeks

ACE inhibitors lower blood pressure, and the most common early complaint is lightheadedness when standing up quickly. Teams usually start at a low dose and increase it in steps over weeks or months, which is why the plan often involves several short follow-ups rather than one appointment and a year of silence.

Expect a blood test roughly one to two weeks after starting and after each dose increase. It checks creatinine, which reflects kidney function, and potassium, which these medications tend to nudge upward. Both are routine checks rather than warnings, and both are the reason the dose moves gradually.

The dry cough that some children develop is not dangerous and does not indicate an allergy, though it can be persistent enough to interfere with sleep. It resolves after switching to an ARB. Cost is rarely the obstacle here, since lisinopril, enalapril, and losartan are all long-established generics.

What to Ask at the Appointment

Three questions get you the specifics that a general recommendation cannot.

• Which drug, at what target dose, and over what timeline? The starting dose is almost never the maintenance dose, and knowing the target tells you how many adjustment visits to plan for.
• Has he had a cardiac MRI, and when is the next one? MRI detects fibrosis that an echocardiogram misses. Most children can hold still for it without sedation by age six or seven, and the result may change the urgency of the plan. The cardiomyopathy monitoring schedule for DMD lays out how imaging intervals shift with age.
• What happens to the plan if next year's echo is still normal? A normal result a year from now is the expected outcome of treatment working, not evidence the medication was unnecessary. Hearing your cardiologist say so in advance makes the next appointment easier to interpret.

One more piece of this conversation belongs to the rest of the family. Some female carriers of DMD develop cardiomyopathy themselves, which is why cardiac screening for carriers is part of standard genetic counseling. If nobody has raised it with your son's mother, aunts, or sisters, raise it yourself.

Starting a heart medication for a heart that tests normally runs against the instinct that treatment follows diagnosis. In DMD the sequence is inverted on purpose, because the diagnosis the echo would eventually deliver is the one nobody can reverse. A broader picture of cardiac care across muscular dystrophy fills in what the years after that first prescription look like. The prescription written at age 10 is targeting the muscle your son still has.