Myocardial ischemia in the presence of normal epicardial coronary arteries can be caused by an abnormality in the microcirculation or myocardial cell or by hypertrophy resulting in depressed coronary vasodilator reserve. Newly developed methods of assessing coronary blood flow and velocity make definitive diagnosis possible. Treatment, which may be difficult, includes therapy for the underlying cause, a calcium blocker, and nitrates.