The Heart and Estrogen-Progestin Replacement Study (HERS) investigated whether hormone replacement therapy could prevent heart attacks and cardiac deaths in postmenopausal women with existing coronary heart disease. This landmark 9-year trial followed 2,430 women who received either combined estrogen-progestin therapy or placebo. The study aimed to determine if hormones, widely prescribed for menopause symptoms, could also provide cardiovascular protection in high-risk women. HERS represented one of the largest controlled investigations into hormone therapy's heart health effects, challenging prevailing medical assumptions about postmenopausal hormone use and cardiovascular disease prevention.
