Comments by "Titanium Rain" (@ChucksSEADnDEAD) on "The Most Painful Death Ever (VIEWER DISCRETION)" video.

Overworking the heart is not good either. What's more likely is that since the muscle fibers are not as fast dividing as mucosa or skin, and it wasn't irradiated, the organ was stable and was only affected by the other symptoms and organ failures.
1