I eat the heart and liver of animals that are not old but always check them for parasites first.
Older animal livers often have at least one of three kinds of parasites (especially caribou) or are very dark and strong tasting (especially bull moose).
I almost always keep the kidneys though. Cut out the centre and soak them a bit = excellent fried.
The ministry here warns against eating the livers and kidneys of Moose, caribou, and deer because of the possibility of cadmium being present (carried by the wind, etc. to wilderness areas from industries in the south) but I ignore that and eat the organ meats in moderation.
I base my opinion on having "gutted", cleaned, cut up or butchered up to 200 big game animals a year (mostly caribou, bears, moose, but much fewer deer) for many years during my professional guiding career. At not quite 70 years old I still work on the animals we harvest and often those of friends.
The people here eat mostly wild game which gives me the opportunity to continue to "study" parasites and the condition of the edible organs (I live on a northern reservation and my wife is Cree).