Hjertstedt enjoyed an outstanding junior career for Sweden, where he was a member of the winning World Amateur Team Championship squad in 1990. He would join the AustralAsian Tour and be named its Rookie of the Year that same year. After a stint on the European Tour, Hjertstedt entered the PGA Tour's Qualifying School, earning an exemption for 1997. That year, he picked up his first PGA Tour win at the B.C. Open.