In the crowded operating room, the surgeons had made the long incision down the middle of the child’s chest, cut the breastbone to spread the rib cage and reach the heart. Then the lights went out.

Generators kicked on to keep life-support equipment running Wednesday night, and nurses and surgical assistants held flashlights over the operating table, guiding the surgeons as they snipped and cut, working to save the child’s life in almost total darkness.

"So far we are coping on our own,” said Borys Todurov, director of the clinic, the Heart Institute, in Kyiv, Ukraine. "But every hour is getting harder. There has been no water for several hours now. We continue to do only emergency operations.”