The heart was always seen as the noblest of the internal organs as well as the most vital. The hearts of martyrs or future candidates for sainthood would be preserved, but never their livers, say, or the entrails - at least not on their own; it was either the heart by itself or the whole lot together.
Your liver is your vital detoxification organ, and if it becomes overloaded with toxins from the food, drink, or medications you're consuming, you'll have more toxins circulating throughout your body, damaging your organs and glands. Detoxing your liver will help it work more efficiently - and help you slim your waistline.
'Meat' is a vague term and can be used to refer to many parts of an animal, including internal organs and skin. For the most part, the meat we eat consists of muscle tissue taken from farm animals, whether it's a sirloin steak, which is cut from the rear of a cow, or a pork chop, taken from flesh near the spine of a pig.