What Is Unstable Angina?

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Unstable angina, a form of acute coronary syndrome (ACS), causes random or unpredictable chest pain as a result of partial blockage of an artery that supplies the heart. In contrast to stable angina, the pain or discomfort of unstable angina often occurs while resting, lasts longer, is not eased with medication, and is unrelated to any obvious trigger, such as physical exertion or emotional stress. Emergency medical attention is necessary.

unstable angina
Verywell / Gary Ferster

Unstable Angina Symptoms

Unstable angina is "unstable" because symptoms may occur more frequently than usual, without any discernible trigger, and may persist for a long time.

The classic symptoms of angina include chest pressure or pain, sometimes squeezing or “heavy” in character, that often radiates to the jaw or left arm.

Keep in mind, though, that many patients with angina do not have classic symptoms. Their discomfort may be very mild and localized to the back, abdomen, shoulders, or either or both arms. Nausea, breathlessness, or merely a feeling of heartburn may be the only symptom.

What this means, essentially, is that anyone middle-age or older, especially anyone with one or more risk factors for coronary artery disease, should be alert to symptoms that might represent angina.

In addition, people without any history of coronary artery disease can also develop unstable angina. Unfortunately, these people seem to be at higher risk of a myocardial infarction (heart attack) because they often don’t recognize the symptoms as angina.

In the end, anybody with a history of coronary artery disease should suspect unstable angina if their angina:

  • Occurs at lower levels of physical exertion than normal
  • Occurs at rest
  • Persists longer than usual
  • Wakes them up at night
  • Is not eased by nitroglycerin, a medication that relaxes and widens coronary arteries

If you think there is any possibility you might have unstable angina, you need to go to your healthcare provider or an emergency room immediately.


As with all forms of ACS, unstable angina is most often caused by the actual rupture of a plaque in a coronary artery. What triggers this is often unknown.

The ruptured plaque and the blood clot that is almost always associated with the rupture form a partial blockage of the artery. This may create a "stuttering" pattern as the blood clot grows and shrinks, producing angina that comes and goes in an unpredictable fashion.

If the clot should cause complete obstruction of the artery, which commonly happens, the heart muscle supplied by that affected artery is in grave danger of sustaining irreversible damage. In other words, the imminent risk of a complete heart attack is very high with unstable angina.

Unstable angina is so-named because it no longer follows the predictable patterns typical of ​stable angina. Obviously, such a condition is quite uncertain and, as such, is a medical emergency.

Unstable Angina
  • Symptoms occur in an unpredictable fashion and without a known trigger.

  • Often occurs at rest and make wake you from sleep.

  • Symptoms can last 30 minutes or more.

Stable Angina
  • Symptoms tend to follow a pattern.

  • Symptoms are typically brought on by exertion, fatigue, anger, or some other form of stress.

  • Symptoms usually last about 15 minutes.


Diagnosis of unstable angina is often done in the emergency room. Symptoms are critically important in making the diagnosis of unstable angina, or indeed, any form of ACS.

In particular, if you have one or more of the following three symptoms, your healthcare provider should take that as a strong clue that a type of ACS is occurring:

  • Angina at rest, especially if it lasts more than 10 minutes at a time
  • New onset angina that markedly limits your ability to engage in physical activity
  • An increase in prior stable angina with episodes that are more frequent, longer lasting, or that occur with less exertion than before

Once your healthcare provider suspects ACS, they should immediately order an electrocardiogram (ECG) and cardiac enzyme testing. High-sensitivity cardiac troponins are the preferred biomarker to detect or exclude myocardial injury (heart cell damage).

The results of these tests, together with review of your symptoms, will help confirm a diagnosis.

Notably, unstable angina and non-ST-elevation myocardial infarction (NSTEMI), a type of heart attack, are similar conditions. In each condition, a plaque rupture has occurred in a coronary artery, but the artery is not completely blocked so at least some blood flow remains.

In both of these conditions, the symptoms of unstable angina are present. The only difference is that in an NSTEMI, enough heart cell damage has occurred to produce an increase in cardiac enzymes.

  • If ST segments—a portion of an ECG—are elevated, a complete blockage of the artery is indicated. If cardiac enzymes are increased, there is cardiac cell damage.
  • If ST segments are not elevated, the artery is not completely blocked. Normal cardiac enzymes indicate no cell damage is present.
ST Segments Cardiac Enzymes Diagnosis
Elevated Elevated "Large" myocardial infarction (MI), a.k.a. an ST-segment elevation MI or STEMI
Not elevated Elevated

"Smaller" MI, a.k.a. a non-ST segment MI or NSTEMI

Not elevated Not elevated Unstable angina


If you have unstable angina, you will be treated with one of two general approaches:

  • Treated aggressively with medications to stabilize the condition, then evaluated non-invasively
  • Treated aggressively with medications to stabilize the condition and given an early invasive intervention (generally, angioplasty and stenting).

Since unstable angina and NSTEMI are so similar, their treatment is identical.


Medications are used to ease chest pain and associated ischemia (when the heart is not obtaining adequate blood flow). Medications to stop blood clot formation within the affected artery are also given.

There are three main types of medications used to treat unstable angina: anti-ischemics, antiplatelets, and anticoagulants.

Anti-Ischemic Therapy

Sublingual nitroglycerin, an anti-ischemic medication, is often given to alleviate any ischemic chest pain.

For persistent pain, intravenous (through the vein) nitroglycerin may be given, assuming there are no contraindications (for example, low blood pressure). Morphine may also be given for persistent pain.

A beta-blocker, another anti-ischemic medication, will also be given as long as there are no contraindications, such as signs of heart failure. This can lower blood pressure and heart rate, both of which, when high, increase the heart's oxygen consumption requirements.

Finally, a cholesterol-lowering medication called a statin, like Lipitor (atorvastatin) or Crestor (rosuvastatin), will be given. These drugs have been found to decrease the rate of heart attacks, death from coronary heart disease, need for myocardial revascularization, and stroke.

Antiplatelet Therapy

Antiplatelet medications, which prevent platelet clumping, will be given as well. This includes both aspirin and a platelet P2Y12 receptor blocker—either Plavix (clopidogrel) or Brilinita (ticagrelor).

Anticoagulant Therapy

Anticoagulants thin the blood. Examples include unfractionated heparin (UFH) and Lovenox (enoxaparin).

Possible Invasive Intervention

Once stabilized with medication, a cardiologist will decide whether a patient needs an invasive intervention, usually angioplasty with stenting (a.k.a. percutaneous coronary intervention, or PCI). This procedure involves the use of a balloon catheter to unblock the artery and the subsequent placement of a stent to prop the artery open.

Determining whether to proceed with angioplasty and stenting is a very important decision. One tool many cardiologists use to help guide this decision is called the thrombolysis in myocardial infarction (TIMI) score.

The TIMI score is based on the following risk factors:

  • Age 65 years or older
  • Presence of at least three risk factors for coronary heart disease (hypertension, diabetes, dyslipidemia, smoking, or a positive family history of an early myocardial infarction)
  • Prior coronary artery blockage of 50% or more
  • At least two episodes of angina in the last 24 hours
  • Elevated cardiac enzymes
  • Use of aspirin in the last seven days

A low TIMI score (0 to 1) indicates a 4.7% chance of having an adverse heart-related outcome (for instance, death, heart attack, or severe ischemia requiring revascularization).

A high TIMI score (6 to 7) indicates a 40.9% chance of having an adverse heart-related outcome and, thus, nearly always warrants an early intervention like PCI.

A Word From Verywell

If you are experiencing new or worsening chest pain or chest pain that will not go away with rest or medication, you need to go to the emergency room right away. Even if your pain turns out to not be heart-related, it's much better to be cautious and get evaluated.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Hamm CW, Braunwald E. A classification of unstable angina revisitedCirculation. 2000;102(1):118-22. doi:10.1161/01.CIR.102.1.118

  3. Gulati M, Levy PD, Mukherjee D, et al. 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline for the evaluation and diagnosis of chest pain: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice GuidelinesCirculation. 2021;144(22). doi:10.1161/CIR.0000000000001029

  4. Antman EM et al. The TIMI risk score for unstable angina/non-ST elevation MI: A method for prognostication and therapeutic decision makingJAMA. 2000;284(7):835-42. doi:10.1001/jama.284.7.835

Additional Reading

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.