This recipe can be done with any large heart. I designed it for deer and elk, but it will work with antelope, moose, wild boar or whatever. For non-hunters, try beef heart, veal heart or lamb hearts. You don't have to marinate the meat, but it adds a lot of flavor, and helps keep it moist on the grill.
A tip on the peppers and onions: Cut them in large pieces so they don't fall through your grill grates. For the onions, make sure you keep the stem end attached. And cook the skin side of the peppers first -- if you get any parts that blacken, the skin peels right off. You actually want significant blackening here, so keep your grill ragingly hot.