Rheumatic heart disease, the No. 1 killer of American children a hundred years ago, is largely gone in this country now. But it's still wreaking havoc in Africa despite the fact it's preventable with antibiotics. Filmmaker Kief Davidson, in his film Open Heart, tells the story of eight Rwandan children who need life-saving cardiac surgery, and the one hospital that can help them. Audie Cornish speaks with Davidson about his Oscar-nominated short documentary.