Her debut in the adult class celebrated the javelin thrower Heli Rantanen 1990 at the European Championships in twelfth with 53.98 m. At the World Championships the following year it was 60.96 m Ninth.
At the Olympic Games in 1992 Heli Rantanen threw the spear in qualifying at 63.98 m. In the final, it was with 62.34 m sixth. In 1993, an eleventh place finish at the World Championships with 53.14 m by 60.56 m in qualifications. Ironically, at the European Championships in Helsinki in 1994 lacked the pitcher due to injury.
At the World Championships in 1995, Rantanen qualified with 60.34 m. For the first time she could then towards the qualification significantly improved and finished in fourth place with 65.04. While the White Russian Natalya Schikolenko clearly won with 67.56 m, were the second-placed Romanian Felicia Tilea Moldovan with 65,22 m and Rantanens country woman Mikaela Ingberg 65.16 m within inches of Rantanen.
The 1996 Olympic Games in Atlanta were the career highlight of Heli Rantanen. With a new personal best of 66.54 she placed second behind the qualification Tilea. In the final, she could easily be increased to 67.94 s and won before the Australian Louise McPaul and the Norwegian Trine Hattestad.
Then to a tenth place finish at the 1997 World Championships with 62.64 m still followed at the European Championships in 1998 a fifth place with 62.34 m.
Finnish athletes have dominated for many years the history of the Olympic athletics crucial, especially in long-distance running and javelin. Heli Rantanen was after 100 years of history of the modern Olympic Games, the first Finnish athlete who was able to win an Olympic victory.