A study of 18,000 men and women is being launched to see if pills containing the nutrients in dark chocolate can help prevent heart attacks and strokes.  The pills are so packed with nutrients that a person couldn't eat enough candy bars to get the same dose...and the pills won't have the sugar or fat.  In smaller studies, cocoa flavanols improved blood pressure, cholesterol, the body's use of insulin, artery health and other heart-related factors.  The study is expected to last four years.