Sprinkle venison with salt and pepper. Melt 2 tablespoons butter in large nonstick skillet over high heat. Working in batches, add venison to skillet and cook to desired doneness, about 2 minutes per side for medium-rare. Set aside. In fat remaining in skillet saute mushrooms with garlic, stirring, until liquid mushrooms give off is evaporated. Add broth, Port, and Worcestershire sauce. Simmer sauce until thickened and reduced to about 3/4 cup, about 15 minutes, and stir in vinegar and salt and pepper to taste. Divide sauce among 4 plates. Place 2 venison medallions a top sauce on each plate.