For umami butter, in a small food processor, blend softened butter, anchovies, miso, celery, parsley and lemon zest for about 30 seconds or until smooth. Set aside.
Rinse beef heart and dry; remove all veins, silver skin and tough bits with a sharp knife. Slice heart into four steaks. Work with the natural form of the heart; don’t worry about having them all the same.
Season steaks with salt and pepper. Over high heat, grill to medium rare. Heart is a lean muscle and does not like to be overcooked.
Rest steaks in warm area for 3 to 4 minutes with 1 teaspoon of butter on each. Once rested, slice against grain of steak to break the long muscle fibers and create a tender cut. Serve sliced heart with crispy fries, a small arugula salad and finish with umami butter slowly melting on top.