Microvascular angina ( previously known as Cardiac Syndrome X ) is a form of angina (chest pain) associated with insufficient blood flow to the heart (and some other organs/regions) but in patients who have normal coronary angiograms.
It's estimated that as many as 30% of patients with angina have this type, rather than 'standard' angina which is caused by narrowing of arteries - typically due to Arterial sclerosis (a.k.a Atherosclerosis)plugin-autotooltip__plain plugin-autotooltip_bigArterial sclerosis (a.k.a Atherosclerosis)
Arterial sclerosis (a.k.a. atherosclerosis) is an extremely common condition which can cause coronary thrombosis, myocardial infarction and other serious conditions. However:
""The atherosclerotic process is not fully understood."
(ref. Hospital Practice Journal Volume 35, 2000 - Issue 2)
There is currently no known specific cause of the condition.
While numerous physiological mechanisms have been proposed, none have been proven.
Source : Wikipedia