Although women can develop heart disease at any age, most women show signs and symptoms of disease about 10 years after men. For years, it has been thought that the reason for this lag is that women's hearts are protected by estrogen, and that when women go through menopause and lose their natural estrogen, they also lose their protection from heart disease. It has been assumed that if estrogen is replaced then protection will continue. These assumptions have not been proven. In fact, three large, randomized trials have shown no benefit from hormone replacement therapy in women known to have heart disease, and in fact have shown that hormone replacement may be harmful.