My son now has an enlarged heart. could that be caused by the previous treatment that cured his wpw?

Unlikely: The typical treatment for wolff-parkinson-white syndrome is radio-ablation of an electrical pathway in the heart. Complication rates for the procedure range from 1.5% - 4% in the literature, but rarely lead to an enlarged heart. More likely however is a genetic association between WPW and congenital hypertrophic cardiomyopathy. Talk with your pediatrician or family doctor about genetic testing.

Possible: Ablation therapy for WPW can -although rare- affect a coronary leading to ischemic heart disease or myocardial infarction. If the dilatation is severe a stress test evtl followed by coronary angiography might be indicated. Talk to your cardiologist.