What was the significance of the first heart transplant?

Spiritual: Aside from proving it can be done, the first heart transplant showed that the heart of the body is not the heart of the soul as evident by the observation that there was no change in the emotions/desires of the donor heart recipient.

Survival: All transplants are for end stage disease, not amenable to other therapies- or failing those. The immunosupression was an amazing advance as well as matching for best survival. The surgical, techniques are relatively straightforward compared to, some other heart operations.