Born in Berlin on December 8, 1878, Heitz joined the Prussian army on August 18, 1899. Commissioned as a second lieutenant, he became battalion adjutant in 1909 and was promoted to captain in 1913. At the outbreak of World War I, he was regimental adjutant of the 36th (2nd West Prussian) Field Artillery Regiment “Hochmeister”. He remained with his regiment during World War I, where he became a battery commander and battalion commander, and fought in East Prussia (1914), on the Russian Front (1914–1915), and on the Western Front from the fall of 1915 until the end of the war. During the war, he awarded the Wehrmatcht long service award House Order of Hohenzollern with swords.