[4] He had thirty amateur fights before making his professional debut on 2 August 1929 at light heavyweight with a points win over former European champion Fernand Delarge.
[5] In November 1930 he beat Dutch champion Piet Brand, and in January 1931 challenged for Ernst Pistulla's German light heavyweight title, the fight ending in a draw.
[1] Later that year he returned to the US for another series of fights, and after five straight victories, including a decision win over NBA world champion George Nichols, in March 1933 he challenged Maxie Rosenbloom for the NYSAC world light heavyweight title at Madison Square Garden;[4][5] Rosenbloom beat a tired Heuser by unanimous decision, inflicting only the second defeat of Heuser's career.
[6] Over the next three years, Heuser beat Hans Schönrath and Arno Kölblin, his only defeats in this period in over thirty fights coming at the hands of Merlo Preciso and Karel Sys.
[1] In February 1938 he beat Sys on points, and the following month stopped Gustave Roth in the seventh round to add the IBU world and European titles.
[10] Heuser was initially ordered to defend this European title against Italian champion Sante De Leo (who had previously accepted a challenge to face Lazek), which prompted the German authorities to threaten to withdraw from the IBU in protest,[10] but in July 1939 Heuser faced Max Schmeling in front of 70,000[11] people at the Adolf-Hitler-Kampfbahn, Stuttgart, with the German and European titles at stake;[12] Schmeling knocked him out in the first round.