Grilled, yes. You can cube it first, then marinate, then skewer and grill. A Peruvian version which I used to do for a tapas table was marinated in vinegar, wine, garlic, cumin and ajis amarillos but you could use other dried or fresh hot peppers instead. Add a little salt and pepper and marinate overnight or all day, depending on when you wish to cook.
Take some of the chilies you used in the marinade and toast and reconstitute them if dried. Puree them with a little fresh water, some of the marinade and a bit of oil, and add salt to taste. Skewer the heart cubes, brush well with the sauce and grill, turning very frequently, till cooked through, over hot coals. They don't take long--maybe 5 min or so. Serve immediately with the remaining sauce. Good with plain rice, spicy beans and mashed roasted plantains with a small side salad.
You could probably do a whole heart in the WSM, slowly, as they're not a medium-rare or even medium item. I think I would marinate/brine in buttermilk with onion, garlic and salt first and might fill with a unsalted butter/milk-soaked breadcrumb mix. Clean of all veins and so forth first, of course.
