Dark chocolate is a form of chocolate containing cocoa solids and cocoa butter without the milk or butter found in milk chocolate. Dark chocolate without added sweetener is known as bitter chocolate or unsweetened chocolate.
Dark chocolate is rich in disease-fighting antioxidants. Studies show it can help reduce blood pressure and lower the risk of heart disease. Studies show that dark chocolate — when it is not loaded with sugar and saturated fat — is indeed a heart-healthy chocolate treat. Wikipedia