This is quite true that endogenous estrogens protect female hearts and vessels prior to onset of menopause, they act as vasodilators, similarly to calcium channel blockers, have favorable effect on lipid metabolism and coagulation. But as for the application of HRT for primary or secondary prevention of CVD, it remains questioable due to the results of recent studies like HERS, WHI, PEPI, NHS, etc. which had demonstrated that selective beneficial effects of HRT on CVS doesnt overweight the possible risk of certain types of cancer, like invasive breast cancer, though decreasing the risk of colon cancer. Besides, HRT increses the overall risk of arterial and venous thrombosis in patients with trombophillia, EVTET trial.

It is not a fact that estrogen protects female hearts and vessels before menopause.  Rates of heart disease and death from heart disease increase with age; there is no abrupt change in the years after menopause.  Etc.  Certain heart disease risk factors seem to increase after menopause, and there is better evidence that surgical menopause increases risk.