1 beef heart, about 1kg | 2.2lb
1/2 cup balsamic vinegar
Salt and pepper to taste, be generous!
Fair amount of cooking fat, ghee, lard or coconut oil

procedure

 
Rinse the heart well under cold running water and pat it really dry.
Cut the heart open (if your butcher hasn’t done that already) and remove any visible strings, arteries and blood vessels that may have been left behind; trim off excess fat and set aside.
Place the heart to marinate overnight in balsamic vinegar.
When you are ready to grill the heart, pat it really dry once again, and sprinkle generously with salt and pepper on both sides.
Cut the heart in half if necessary, so it fits in your skillet (or if you want to save some of it for another recipe)

Melt a fair amount of cooking fat in a large heavy skillet set over high heat. Grill the beef heart without moving the meat for 5-6 minutes per side, or until a nice golden crust forms.
Remove the meat to a plate, tent loosely with aluminum foil and let it rest for 15 minutes.
Slice fairly thinly against the grain and serve.