In 1999, a Swedish medical student named Anna Bagenholm lost control while skiing and landed head first on a thin patch of ice covering a mountain stream.
Bagenholm was the very definition of clinically dead: Her circulatory and respiratory systems had gone quiet for just over three hours before she was brought back to life. But what was happening in her body on a cellular level during the hours she went without a heartbeat? Were her tissues dying along with her consciousness? And how much longer could she have gone with no blood circulation?