Heitzmann was born on 2 October 1836 in Vinkovci, Austrian Empire to a Jewish family.
After graduation, he furthered his studies in Vienna with Franz Schuh (1804–1864), Ferdinand Hebra (1816–1880), Salomon Stricker (1834–1898), and Carl Rokitansky (1804–1878).
[2] Here, he established a laboratory for microscopical research, and became one of the founders of the American Dermatological Association (ADA).
Heitzmann is credited for being the first physician to describe the precursor corpuscles of red cells, structures that he referred to as hematoblasts.
In 1872 he documented his findings in a treatise titled Studien am Knochen und Knorpel, in which he mentions that his discovery of the hematoblast was in the bone marrow of an injured dog's leg.