Heikkinen first appeared internationally at the Junior World Championships 2002 in Schonach . Over the distance of 10 kilometers freestyle he was the best Finnish participant in eighth place (in the sprint he was only 38th). He was able to improve this result a year later at the Junior World Championships 2003 in Sollefteå over 10 km classic by one place, while he was 42nd in the freestyle race over 30 kilometers. This made it possible for him to take part in the cross-country skiing world cup , where he could not convince with places far outside the world cup points. In the 2004/05 season he succeeded for the first time in the 30 km freestyle in Ramsau to gain a World Cup point. Nevertheless, Heikkinen was still rarely used in the World Cup. It wasn't until the 2007/08 season that he achieved his breakthrough in the World Cup. In his home town of Lahti , he was ninth in a classic surprise over the distance of 15 km. At the World Cup final in Bormio , he was able to confirm this result. In the prologue over 3.3 km freestyle he came in 13th place and was able to secure 14th place in the overall standings with the fastest time of all participants in the final pursuit competition over 15 km freestyle.
Also at the start of the 2008/09 season Heikkinen was in the squad of the Finnish World Cup team and was able to convince over 15 km freestyle with a 19th place as well as with the Finnish relay, in which he was the third runner to hand over to the bottom runner. At the Tour de Ski 2008/09 he came in 26th. His greatest success so far was at the Nordic World Ski Championships in Liberec in 2009 . Heikkinen won the bronze medal over 15 km in classic style. A week later he secured the bronze medal in the relay together with Sami Jauhojärvi , Teemu Kattilakoski and Ville Nousiainen . He also took eleventh place over 30 kilometers in the skiathlon and 37th place over 50 kilometers in free technique. At the end of the season he came in 19th place at the World Cup finals in Falun and reached 30th place in the overall World Cup and 19th place in the Distance World Cup. After third place over 15 km freestyle in Beitostølen at the beginning of the 2009/10 season , he won his first World Cup victory in Davos over 15 km freestyle. He finished the Tour de Ski 2009/10 in 12th place. He came three times in the top ten, including third place in the pursuit race in Oberhof . At the season highlight, the 2010 Winter Olympics in Vancouver , he finished 39th over 15 km freestyle and fifth in the relay. At the end of the season, he finished 24th at the World Cup finals in Falun and reached 13th place in the overall World Cup and ninth place in the Distance World Cup. The following season he won the Tour de Ski 2010/11 , which he ended prematurely, in the pursuit race in Oberstdorf . In February 2011 he celebrated his greatest success so far when he became world champion over 15 km in classic style at the Nordic World Ski Championships 2011 in Oslo . He also achieved 18th place in the skiathlon and fourth place in the relay. In March 2011, he finished 21st at the World Cup finals in Falun and reached 25th place in the overall World Cup and 18th place in the Distance World Cup. After two top ten placements at the beginning of the 2011/12 season , he finished 24th in the 2011/12 Tour de Ski . He finished the season in 44th place in the overall World Cup. At the beginning of the following season he finished 18th at the Nordic Opening in Kuusamo and second at La Sgambeda . In January 2013 he became Finnish champion in the 15 km freestyle. His best results at the Nordic World Ski Championships 2013 in Fiemme Valley were 12th place over 15 km freestyle and fifth place with the relay. Over 20 kilometers he was 25th in classic technique and 17th in the skiathlon. In March 2013 he came in 18th place at the World Cup finals in Falun and reached 39th place in the overall World Cup. In the 2013/14 season he finished 17th at the Nordic Opening in Kuusamo and ninth place at the World Cup finals in Falun. His best results at the 2014 Winter Olympics in Sochi were 15th in the 50 km mass start race and sixth in the relay. In March 2014 he became Finnish champion in the 10 km freestyle and at the end of the season he finished 28th in the overall World Cup and 19th in the Distance World Cup. After seventh place at the Nordic Opening in Lillehammer at the beginning of the 2014/15 season , he won two wins at the Scandinavian Cup in Östersund . At the following World Cup in Ryybinsk , he won third place in the skiathlon. At the Finnish championships in Jämi and Ruka he was champion over 15 km freestyle and over 50 km freestyle. His best placings at the 2015 Nordic World Ski Championships in Falun were 16th in the skiathlon and eighth in the relay. Over 50 kilometers in the classic technique he was 20th and over 15 kilometers in the free technique he reached the 21st place. He finished the season in 20th place in the overall World Cup and in 14th place in the Distance World Cup.
The following season, Heikkinen came 18th in the 2016 Tour de Ski . In January 2016 he became Finnish champion over 15 km freestyle in Imatra, as in the previous year. He finished the Ski Tour Canada , which was held for the first time, in sixth place. He finished third in the skiathlon in Canmore and second in the final stage. He also won the 15 km freestyle and at the end of the season finished 17th in the overall and in the distance World Cup. With the Finnish cross-country relay, he was fourth just one place behind precious metal. In April 2016 he won at the Finnish championships in Taivalvaara over 7.5 km classic and the gold medal in the subsequent pursuit.
After ninth place over 15 km classic in Ruka at the first World Cup of the 2016/17 season, he came third in the World Cup mini tour in Lillehammer . He won the final chase stage over 15 km classic. At the following World Cup in Davos , he achieved third place over 30 km freestyle. He finished the Tour de Ski 2016/17 in fifth place. He achieved third place in the 15 km mass start race in the Fiemme Valley and also ran the second fastest time on the final stage. In February 2017 he finished second over 15 km classic at the Finnish championships in Keuruu . At the season highlight of the Nordic World Ski Championships 2017 in Lahti , he won the bronze medal in the 50 km mass start race. He also came in 18th place in the skiathlon, 11th place over 15 km classic and fifth place with the relay. At the end of the season, she finished 24th in the World Cup finals in Québec and reached fifth place in the overall World Cup and third place in the Distance World Cup. His best placings at the 2018 Winter Olympics in Pyeongchang were tenth place over 15 km freestyle and fourth place with the relay. In the skiathlon he was 21st and in the final 40-kilometer race in the classic technique he was 25th. At the Nordic World Ski Championships in 2019 in Seefeld in Tirol , he ran to 12th place in the skiathlon , 11th place in the 50 km mass start race and fourth place with the relay.
Finland
Davos
Oberstdorf
Canmore
Lillehammer
Falun