In a large skillet, saute steaks in butter for 2 minutes on each side or meat is no longer pink; drain.
In a small bowl, combine the grape juice, Worcestershire sauce and mustard; stir into cooking juices. Bring to a boil; cook for 1 minute. Remove steaks and keep warm. Cook the sauce 1-2 minutes longer or until thickened. Season with salt and pepper. Serve over cube steaks.