[1][2] Heikinheimo enrolled as a student at the Finnish Co-educational School in Oulu in 1913 and joined the North Ostrobothnian Association.

He took part in the fighting in the First World War on the eastern front of Germany on the Misse, the Gulf of Riga and the Aa.

[1][2] He arrived in Finland with the command of the oberzugführer Friedel Jacobsson on January 30, 1918, and joined the Perä-Pohjola Conservation Corps in Tervola.

He led his battalion to battles in Vilkkilä, Haavisto (Orivesi), Tervaniemi, Lempäälä, Vesilahti, Karku and Tyrvää.

From August 12, 1926, he served as commander in the Jääkäri Brigade, from where he was promoted to Division 3 on June 9, and was assigned as an infantry inspector.