CT Coronary Angiography: What It Shows and What to Expect

What are the coronary arteries?

The heart muscle requires its own blood supply.

This is provided by the coronary arteries.

The main vessels include:

• —left main coronary artery
• —left anterior descending artery
• —circumflex artery
• —right coronary artery.

Over time, atherosclerotic plaque can develop within the walls of these arteries.

This process is known as coronary artery disease.

What is coronary artery disease?

Coronary artery disease develops when atherosclerotic plaque builds up within the coronary artery walls.

Plaque may contain:

• —cholesterol and lipid
• —inflammatory tissue
• —fibrous tissue
• —calcium.

As plaque increases, it can narrow the artery.

Some plaques may also become unstable and contribute to formation of a blood clot, which can cause a heart attack.

What can CT coronary angiography show?

Modern CT coronary angiography can assess:

Coronary artery plaque

CT can identify both calcified and non-calcified atherosclerotic plaque.

Coronary narrowing

The scan can estimate how much plaque narrows the artery.

Coronary anatomy

It can show how the coronary arteries originate and travel around the heart.

Other cardiac findings

Depending on the scan and clinical question, the examination may also provide information about structures such as:

• —the aortic root
• —ascending aorta
• —heart chambers
• —valves
• —surrounding structures.

Why might I be referred for CT coronary angiography?

Common reasons include investigation of symptoms that might represent stable angina.

NICE recommends 64-slice-or-above CT coronary angiography when clinical assessment suggests typical or atypical angina, and in some people with non-anginal chest pain but relevant ECG abnormalities.^[1]

CTCA is also used in other selected situations, including assessment of coronary anatomy and particular structural-heart or pre-operative questions.

Is CTCA the test used during a heart attack?

Usually not.

If somebody may be experiencing an acute coronary syndrome or heart attack, they require urgent clinical assessment, ECG testing and blood tests such as troponin.

NICE specifically advises that CT should not routinely be used to diagnose acute coronary syndrome.^[1]

CT coronary angiography vs calcium score

These are related but different examinations.

Coronary calcium score

Usually:

• —no contrast injection
• —measures calcified plaque
• —produces an Agatston score
• —mainly provides information about overall coronary atherosclerotic burden and cardiovascular risk.

CT coronary angiography

Usually:

• —uses intravenous iodinated contrast
• —directly images the coronary arteries
• —shows both calcified and non-calcified plaque
• —assesses coronary narrowing
• —provides detailed coronary anatomy.

Someone can therefore have non-calcified coronary plaque even with little or no coronary calcium.

How should I prepare?

Preparation varies between hospitals.

Your department may give specific instructions regarding:

• —food
• —fluids
• —caffeine
• —smoking or nicotine
• —medications
• —arrival time.

Some NHS departments ask patients to avoid caffeine before CT coronary angiography because a slower, more regular heart rate can improve image quality.^[2]

What should I tell the department beforehand?

Tell them if you:

• —are pregnant or could be pregnant
• —have kidney disease
• —have previously reacted to iodinated CT contrast
• —have significant asthma
• —take certain heart medications
• —take medicines for erectile dysfunction such as sildenafil or tadalafil
• —have problems with very low blood pressure
• —have particular heart-rhythm problems
• —have been told to restrict your fluid intake.

This information can be important because medications may be administered as part of the examination.

Why does my heart rate matter?

The coronary arteries move continuously with the beating heart.

CT therefore synchronises image acquisition with your ECG.

A slower, regular heart rate often makes it easier to obtain sharp images of the coronary arteries.

If your heart rate is higher than ideal, you may be given medication called a beta blocker before the scan.

Beta blockers slow the heart rate.

Not everyone needs one.

Your healthcare team will decide whether it is safe and appropriate for you.^[2,3]

Why might I be given GTN?

Many departments administer glyceryl trinitrate (GTN) shortly before the scan.

GTN dilates the coronary arteries, making their lumen easier to assess.

It is usually administered under the tongue.

Possible temporary effects include:

• —headache
• —dizziness
• —lower blood pressure
• —flushing.

What happens during the scan?

The usual process is:

• —1. A cannula is inserted — this allows contrast to be injected.
• —2. ECG electrodes are attached to your chest — these allow the CT scanner to synchronise with your heartbeat.
• —3. Your heart rate and blood pressure are checked — medication may be given if necessary.
• —4. You lie on the CT table — you will practise breath-holding instructions.
• —5. GTN may be given — this helps dilate the coronary arteries.
• —6. Contrast is injected — this makes the arteries visible.
• —7. The images are acquired — you will normally need to hold your breath briefly while the scan is performed.

The actual acquisition is very fast, although the overall appointment can be longer because of preparation and medication. NHS patient information commonly describes total scanning appointments in the region of tens of minutes rather than hours.^[2]

What does the contrast feel like?

During the injection you may experience:

• —warmth through the body
• —a metallic taste
• —a sensation that you are passing urine.

These sensations are common and usually disappear quickly.^[2]

Does CTCA involve radiation?

Yes.

CT coronary angiography uses X-rays and therefore involves ionising radiation.

Modern scanners and ECG-gated techniques allow radiation exposure to be substantially reduced compared with older-generation cardiac CT.

The exact dose varies according to:

• —scanner
• —heart rate
• —body size
• —scan protocol
• —clinical question.

The examination should only be performed when the anticipated clinical benefit justifies the radiation exposure.

What happens after the scan?

Your pulse and blood pressure may be checked again if medication was administered.

Most people can then leave shortly afterwards.

You should follow the specific advice given by the department regarding:

• —driving
• —hydration
• —medications
• —activity afterwards.

Who interprets CT coronary angiography?

The images are interpreted by clinicians with appropriate expertise in cardiac CT, commonly specially trained radiologists and/or cardiologists.

A coronary CT study contains far more information than the initial images you may see on the scanner.

The reader assesses the coronary arteries segment by segment and may use multiple reconstructions to evaluate:

• —plaque
• —narrowing
• —anatomy
• —image quality
• —other relevant findings.

What might my result say?

A report may describe:

No coronary artery disease

No visible coronary plaque or significant abnormality.

Non-obstructive coronary artery disease

Plaque is present, but it is not causing a severe anatomical narrowing. This is still important because it confirms the presence of coronary atherosclerosis.

Moderate or uncertain narrowing

Further functional assessment may sometimes be needed to determine whether the narrowing is actually restricting blood flow. NICE recommends functional assessment when CTCA demonstrates coronary disease of uncertain functional significance or when CTCA is non-diagnostic.^[1]

Significant coronary artery disease

More severe narrowing may require specialist cardiology assessment and potentially further investigation or treatment. The significance depends on which artery is involved, the degree of narrowing, symptoms and the wider clinical picture.

What is FFR-CT?

In selected cases, CT coronary angiography data can undergo additional computer analysis to estimate whether a coronary narrowing is likely to restrict blood flow.

This is known as CT-derived fractional flow reserve (FFR-CT).

It can sometimes reduce the need for invasive testing.

Not every scan or patient is suitable for this analysis.

Why has CTCA become so important?

Large trials have shown that incorporating coronary CT angiography into the assessment of stable chest pain improves diagnostic certainty and can alter preventive treatment.

In the SCOT-HEART trial, CTCA-guided care improved diagnosis and was associated with lower rates of coronary heart disease death or non-fatal myocardial infarction at five years.^[4]

Follow-up published in 2025 demonstrated sustained benefits over approximately ten years.^[5]

Questions to ask after your scan

You may find it useful to ask:

• —Did the scan show coronary plaque?
• —Was the plaque calcified, non-calcified or mixed?
• —Is there any significant coronary narrowing?
• —Do I need further testing?
• —Does this change my cardiovascular prevention plan?
• —Should my cholesterol treatment be reviewed?
• —Should my blood pressure or other risk factors be addressed?

The key message