Today’s invasive cardiologist views disturbances in coronary flow from narrowing of epicardial arteries, as seen in a coronary arteriogram. Impairment in coronary flow is attributed to narrowing of the arteries, and relief sought through angioplasty or bypass surgery.1 This is not sufficient to explain angina, particularly in older women, nor the medical approaches that can be directed at its relief.2

Blood flow to the heart is different from blood flow to other parts of the body in that rhythmic contraction of the left ventricle throttles blood vessels during cardiac contraction; in consequence, blood can only enter the left ventricular (LV) arteries during cardiac diastole. This is readily seen in left anterior descending coronary flow tracings as originally recorded by Gregg et al in conscious dogs with implanted flow meters,3 but can now be recorded in humans non-invasively with ultrasound.4 Such tracings do show some forward blood flow in systole, but this can be accounted for by systolic distension of the epicardial coronary arteries5; essentially there is no systolic flow into the LV myocardium. Hence one needs to consider factors other than coronary narrowing; these include the duration of diastole6 and the pressure gradient across the coronary bed.7 Arterial stiffening can affect both of these, and can readily explain angina even in the absence of coronary narrowing.5^–9 Cardiologists are apt to explain such syndromes as due to “microvascular …