Trim excess fat from the top of each lamb or goat heart, then cut into bite-sized pieces and mix with the ingredients for the marinade/rub. Allow the meat to marinate for at least a few hours and up to 24 hours.
Cooking
To cook the heart skewers, thread the marinated chunks of heart onto a skewer, depending on how many people will be eating you might use larger or smaller skewers.
Heat a grill or griddle, lightly oil it, then cook the skewers for 2 minutes on each side, flipping after each side starts to brown and look slightly charred. You want the finished, cooked heart to be about medium doneness-hot and pink throughout.
Remove the heart skewers from the grill or griddle and serve with cooked potatoes, cilantro, and wedges of fresh lemon if using.
Notes
Any heart can be used here, but lamb are traditional.