Each child had already undergone at least three open-heart surgeries. They’d endured countless hours in doctors’ offices and hospitals after being born with a serious heart condition. But this fall the kids tried a new, very different tactic to boost their wellness: They joined a choir. Fourteen children from ages 8 to 16 with a condition called single ventricle circulation, or “Fontan” circulation, met once a week for two months to learn singing and breathing techniques and practice songs for a winter concert at Northwestern University.