Coronary microvascular dysfunction refers to abnormal dilation and constriction of the small blood vessels in the heart.

The small blood vessels in the heart, called the coronary microvasculature, carry most of the blood flow to the heart muscle, delivering oxygen. These blood vessels can become unhealthy when there is damage to their inner lining. There can also be plaque buildup in the larger coronary arteries that does not narrow them but can contribute to abnormal blood flow. Over time, this leads to abnormal widening or narrowing of the small vessels in response to exercise or stress, which can cause problems with the blood supply to the heart, causing chest pain, shortness of breath, heart attack, and heart failure.

Conditions that increase a person’s risk of having coronary microvascular dysfunction are high blood pressure (hypertension), diabetes, high cholesterol, smoking, autoimmune disease, and prior breast cancer treatment, as well as other unknown factors.