Oscar Heiden was born in either 1868 or 69 and was the child of Christoph Ludwig Friedrich "Ludwig" Heiden and his second wife who was Swedish.

Ludwig, who had moved from Germany to Sweden was a younger brother of August Heiden's mother, Maria Heiden. Therefore, he was an uncle to August and his half-sister, Fredericka (Heiden) Schmidt.

On January 27, 1883, Ludwig sent a letter to his nephew, August Heiden in America containing this information. Oscar would have been August's first cousin.