Use a very sharp knife to trim off all of the fat, sinew, and veins from the heart, including inside surfaces. Have a beer ready, this takes a while.
Cut the heart into small strips about 2 inches thick.
Whisk together all of the ingredients in a medium bowl.
Put the meat into an airtight container dish and cover with anticucho sauce (reserve the remaining ½ cup sauce for serving). Cover and refrigerate the marinated heart for 2 or 3 days, and flip the meat once while it marinates.
Remove the meat from the refrigerator 2 hours prior to grilling.
Prepare the grill for direct, high-heat cooking.
Weave 3 or 4 strips of the beef heart onto the skewers.
When the grill is white-hot, cook a few skewers of meat at a time. The bottom side should get nice and seared after 3 to 4 minutes. Flip the skewers and continue to grill the heart until it is seared on the other side but still medium-rare, about 2 minutes more. (Pro tip: don’t overcook these or they’ll be tough and rubbery)
Serve the skewers with the reserved anticucho sauce.
