The Difference Between Unstable Angina and Stable Angina (Stable Coronary Artery Disease)

Stable angina is chest pain due to cholesterol buildup in the lining of the heart arteries. This cholesterol buildup narrows the blood vessels. Normally when a person exercises strenuously the amount of blood that flows through the heart arteries goes up 4 times or more of the amount of blood that flows when the heart is resting.

The narrowed blood vessels from cholesterol buildup can’t increase blood flow as a normal diameter heart artery can. Thus the heart muscle doesn’t have enough blood to fuel its pumping and the patient gets symptoms, say chest pain or shortness of breath. The symptoms of stable angina may vary a little from day to day in how much exercise or stress it takes to bring on the symptom(s). But the symptoms promptly go away when the stress goes away.

Unstable angina is different in symptoms and in cause from stable angina.
“Unstable angina is characterized by a sudden worsening of angina symptoms, which become more frequent, more prolonged, and more severe and/or occur at a lower threshold or at rest.”*

In unstable angina, a blood clot forms on top of an area of cholesterol build up in a heart artery. The cholesterol buildup (the amount of narrowing) where the blood clot forms may be very mild. In fact, before the blood clot forms cholesterol buildup (the plaque) may not cause any decrease in blood flow with exercise.

But the blood clot can grow until partially or even completely obstructs blood flow in the heart artery. Sometimes, the body’s own clot dissolving system will dissolve the clot and the pain will go away, only to return if the blood clot reforms. This is the reason why the chest pain can come and go even while the patient is doing nothing.

If the blood clot grows to completely obstruct blood flow and it does not dissolve, then the patient can suffer a myocardial infarction. The lack of blood flow to a part of the heart muscle causes heart muscle death, a myocardial infarction (a heart attack).

Patients who have stable coronary disease or stable angina are at risk of developing unstable angina. If the covering over the cholesterol buildup erodes, then a blood clot can form.

Acute coronary syndrome means sudden heart symptoms due to a blood clot forming on a plaque. There are three possibilities when the blood clot and blockage of the heart artery occurs.

If the blockage is complete and occurs in a part of the heart artery that supplies a large amount of heart muscle then an ST elevation myocardial infarction STEMI) occurs. Without immediate treatment, either an angioplasty/stent or clot dissolving medicine, serious heart damage or even death can occur.

If the blood clot blockage shuts off blood to a smaller amount of heart muscle, causing a smaller amount of heart muscle death, then the heart attack is called a non-ST elevation myocardial infarction (Non-STEMI).

Finally, if the blood clot breaks up and reforms and breaks up before any heart muscle dies we call this unstable angina. A person with unstable angina may be at high risk of heart attack damage or death. Many people who ultimately have a heart attack have unstable angina for days or weeks before the heart attack.

This is why a person with new or changing chest discomfort or other symptoms needs to go to the emergency department right away. The emergency doctor can determine whether the patient’s symptoms are due to heart disease and if they are, the doctors can prevent heart damage and prevent death.

Thus, all three of these manifestations of Acute Coronary Syndrome (ACS), unstable angina, STEMI, and Non-STEMI require emergency evaluation and treatment.

*Guidelines on the management of stable angina pectoris  2010 from the European Society of Cardiology available at

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