Oscar or Oskar Heiden was born October 5, 1867 and was the child of Christoph Ludwig Friedrich "Ludwig" Heiden and his second wife, Carolina Grongvist, who was Swedish. Oskar's birthplace was Kristianstad, Sweden.

Carolina was born on July 10, 1832 in Gustaf Frea Lommedtro, Sweden.

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.