Soak about 20 bamboo skewers in cold water before you start your prep, in order to help keep the skewers from burning on the grill.
Trim the beef heart of all excess veins, membranes or fat. Cut into the longest strips possible, about 1/8-inch thick.
Carefully skewer the heart pieces on the bamboo skewers, weaving them and stretching them out to reduce the ruffles. Place in a shallow dish.
To make the marinade, whisk the olive oil, vinegar, mustard, garlic, salt and some pepper in a bowl. Pour the marinade over the heart skewers and let sit for at least 10 minutes.
Preheat the grill to very high heat (you can also use a cast-iron skillet or grill pan over high heat). Place the heart skewers on the grill and cook for about 1 to 2 minutes on each side. Flip when marked and colored nicely.
Serve warm, with a drizzle of olive oil and an optional sprinkling of fresh herbs.
This recipe was provided by a professional chef or restaurant and may have been scaled down from a bulk recipe. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.