I donate all deceased reptiles from my rescue or the ones that patients of the surgical clinic sign over to the University of Pennsylvania's genetics labs so that hopefully they can get a grant to map reptilian genomes. They do see lots of broken chains in the genes of the beardies and corns I donate.
But until they get the funding and the samples needed to map the genome we don't know how much is inbreeding vs. mutations that occured on incubation. Most of the tissue samples they are researching right now are from unhealthy individuals, they need tissue samples from thousands of healthy ones for comparison.
That weak heart example doesn't pan out that much in real life. Most vital organ defects are acquired rather than genetic, and even when genetic that's generally a recessive trait. If there is that large a pool of recessives getting together and furthering weak hearts in their offspring, that's a sign of a bigger problem than just letting the weak ones survive. Just where did all those recessive genes suddenly come from?
True weak hearts from birth are very rare, all those heart attack survivors are generally folks with lifestyle-related problems. Children learn bad habits from their parents and the lifestyle-related problem is passed down, but not genetically.
When you do find a true congenital defect, many of those are the result of a problem when the embryo was forming, and that's not going to pass down to the next generation.
The Zombie Mama is here!