The term "Texas heart shot" was joke and had no definitive birthday. It has never been suggested as a good shot placement.
First time I heard of it was back the 60s when a popular hunting magazine writer was spoofing a buddy for taking a long range shot at the only place he could clearly see; it struck a lot of guys as a good bit of humor so some of us started using ourselves. It never occured to me that anyone would ever take it serious.
On the other hand, I have a "young" friend who got a .338 WM and loads Noslers so he can get a rack from a Georgia white tail from any angle he encounters. It works too but, Lordy, what a mess it leaves.