I have experience with quite a few in vitro models. Perfused and superfused cardiac tissue models (fresh) and there are some tissue media models out there. You need a dye (referenced in some of the publications that I was involved in) to grab the full depth of thermal damage. The tissue replacement media is a direct measure, but isn't as well accepted by clinicians. There is a thigh muscle model as well, but you have to account for the directional nature of the muscle fibers. Heat will conduct down a long muscle fiber whereas cardiac muscle is more amorphous.