Although unsuccessful at creating a genetic copy of the extinct species, they developed a look-alike breed with grullo coloration and primitive markings.

The gait of the Heck horse is high stepping, which makes them comfortable to ride and which is considered attractive while being driven.

[7] The Heck brothers bred together several European small horse and pony breeds hypothesized to be descended from the tarpan.

[2] The initial crosses were made between Gotland and Icelandic mares (who visually closely resembled the tarpan, especially in the shape of the head) and Przewalski's horse stallions (who provided the desired dun coloration and upright mane), and the offspring were then bred to each other.

[6] During World War II, horses of the desired type were taken from German-occupied countries to use in the Hecks' breeding program.

Vetulani considered this a "baffling campaign of destruction", and the Hecks' actions effectively ended his breeding program.

[8] Some of the resulting Heck horses were sent back to Białowieża, to become part of a hunting preserve for Nazi government officials.

[8] The first Heck horse in the United States was a stallion named Duke, imported in 1954 by the Chicago Zoological Park in Illinois, followed by two mares in 1955.

[2] In the early 1960s, the North American Tarpan Association was founded by Heck horse enthusiasts to promote the breed.