How Blood Pressure Pill Prevents Heart Attacks By EMMA ROSS    MUNICH, Germany (AP) -- Scientists have unraveled one of the mysteries of precisely how a popular type of blood pressure pill protects against heart attacks, showing it not only lowers blood pressure but also directly improves the health of the artery walls.    Doctors had suspected that blood pressure reduction alone could not explain the whole benefit of the pills, called angiotensin converting enzyme, or ACE, inhibitors, because studies have shown they prevented heart attacks and deaths even in patients with normal blood pressure or those whose high blood pressure did not budge...