Exultavit cor nostrum is a letter, also known as a Papal bull, from Pope Urban IV to the Mongol Ilkhanate leader Hulagu in 1263/1264. The letter was evidently in response to a message brought to Urban by John the Hungarian, who claimed to be the Mongol envoy (it was not uncommon for individuals to present themselves as envoys, even when they were not). According to John, Hulagu desired to become a Christian, and requested that Urban send a representative who would help to baptise him.