Dr. Kilmer McCully takes another look at the cholesterol theory of heart disease in his new book, "The Heart Revolution: The B Vitamin Breakthrough that Lowers Homocysteine, Cuts Your Risk of Heart Disease, and Protects Your Health" (HarperCollins). McCully writes that the real culprit in heart disease is the amino acid homocysteine which is found in the blood. Too much of it can lead to damaged arteries, leaving them susceptible to cholesterol and fat deposits. McCully writes that vitamin B deficiency leads to too much homocysteine.