in women who do have underlying heart disease, estrogen can potentially be harmful—it can induce inflammation in existing arterial plaques, causing a stable plaque to rupture, and it can also promote bleeding into the plaque, both of which can block critical coronary arteries. Estrogen, with or without progesterone, may also cause platelet clumping, which can further obstruct coronary arteries. After the first year of hormone therapy, women no longer have an increased risk of cardiovascular events—even women with preexisting coronary artery disease.
