Isac Viana Santos (born 13 December 1990) is a Brazilian volleyball player. He is part of the Brazil men's national volleyball team. On club level, he plays for Sada Cruzeiro. Silver medallist of the 2018 World Championship, gold medallist of the 2019 World Cup, five–time Brazilian Champion (2014, 2015, 2016, 2017, 2018).