Clean beef hearts thoroughly, removing all gristle, fat and skin, and cut into small pieces, approximately 1 1/4-inch cubes. Put in a large non-reactive bowl.
Toast cumin seeds in a dry frying pan for 2-3 minutes, careful not to burn them and then coarsely crush with a spoon. Add crushed cumin, crushed garlic and remaining dry ingredients to meat and mix well.
Add vinegar and 1/2 cup water to cover the meat and mix thoroughly. Tightly cover bowl with a lid or plastic wrap and marinate for 3 to 4 hours, stirring occasionally.
Once meat is marinated, reserve marinade liquid and set aside.
To make the basting sauce, heat the oil in a medium saucepan. Add the ground chile, salt, pepper and 1 cup of the reserved marinade. Bring to a boil and simmer for 2 to 3 minutes.
Slip three to four pieces of marinated meat on each metal skewer. Heat grill or barbecue and lightly brush with oil.
Place skewered meat on hot grill and baste with marinade. Cook for 2 to 3 minutes, turning and basting often. Serve hot off the grill.