I have learned that one whitetail heart basically will only make about 3 soft tacos, so I supplement with deer liver.
I prepare the heart first by cutting off any fat and tough skin on the outside. I then cut out the stringy connective tissue around the heart cavity. After doing that I then dice the meat into roughly 1/2" x 1/2" pieces. I sprinkle a little salt on the meat after cutting.
I melt butter in a skillet and then sauté minced garlic in the butter. Brown the heart meat in the butter and garlic sauce.
After the meat is brown I deglaze the skillet using the liquid of my choice and simmer the meat until the liquid evaporates. My current favorite is a margarita mix. I find it gives a nice flavor profile typical of traditional Mexican cuisine and leaves a nice rich coating on the meat. We eat this on warm tortillas typically with just cilantro and diced onion (although sometimes we add sour cream).