dilated cardiomyopathy

Imagine a balloon that has been over-inflated so many times that its rubber is stretched thin and limp: when you squeeze it, it barely pushes air out. In dilated cardiomyopathy the main pumping chamber, the left ventricle, becomes enlarged and its walls contract weakly, so each beat ejects only a small fraction of the blood inside. This is the most common form of cardiomyopathy and a leading reason younger adults need heart transplants.

Mechanically, the ventricle dilates and its squeezing strength (contractility) falls, dropping the ejection fraction — the percentage of blood pumped out per beat. Blood backs up into the lungs and body, producing the breathlessness, fatigue, and swelling of heart failure. The stretched chamber and scarred muscle also create electrical instability, raising the risk of dangerous ventricular rhythms.

Causes are many: inherited gene mutations, prior viral myocarditis, heavy alcohol use, certain chemotherapy drugs, thyroid disease, and pregnancy, among others; in a large share of cases no clear cause is found (idiopathic). Treatment targets the underlying cause where possible and uses heart-failure medications that, over months, can sometimes shrink the chamber and improve function — a process called reverse remodeling.