MRI Scan for Heart Conditions

Heart disease is the second leading cause of death in the UK, responsible for around 160,000 deaths each year. Cardiac MRI (CMR) is the gold standard imaging test for assessing heart muscle structure, function, and tissue composition — providing information that no other test can match. It shows the heart beating in real time, measures how well it pumps, detects scarring and inflammation, and can identify the cause of heart problems with remarkable precision.

If you have been told you may have a heart condition, have unexplained chest pain, shortness of breath, palpitations, or a family history of cardiomyopathy or sudden cardiac death, a cardiac MRI can provide answers that echocardiography (heart ultrasound) and other tests cannot.

What Cardiac MRI Can Assess

Cardiac MRI is uniquely capable of:

• Heart muscle function — measuring the ejection fraction (the percentage of blood pumped out with each heartbeat), chamber volumes, and wall motion abnormalities. Normal left ventricular ejection fraction is 55-70%.
• Tissue characterisation — this is where CMR stands apart from all other cardiac imaging. Late gadolinium enhancement (LGE) shows scarring and fibrosis within the heart muscle. The pattern of scarring tells the cardiologist the cause:
  • Subendocardial or transmural enhancement following a coronary territory — previous heart attack (myocardial infarction). The extent of scarring predicts whether the damaged area can recover.
  • Mid-wall enhancement — dilated cardiomyopathy, myocarditis, sarcoidosis.
  • Patchy or epicardial enhancement — myocarditis (heart muscle inflammation).
  • Diffuse subendocardial enhancement — amyloidosis.
• Inflammation detection — T2-weighted imaging and T2 mapping show oedema (swelling) in the heart muscle, indicating active inflammation. Combined with LGE, this helps diagnose acute myocarditis and assess disease activity in inflammatory conditions.
• T1 mapping and ECV (extracellular volume) — newer quantitative techniques that detect diffuse fibrosis and infiltration (amyloid, iron overload) even before LGE becomes positive.
• Valve disease — CMR can quantify the severity of regurgitant valve disease (leaking valves), particularly aortic and mitral regurgitation. It is considered the reference standard for regurgitation volume measurement.
• Congenital heart disease — CMR is essential for assessing complex congenital heart conditions, shunts (abnormal connections between heart chambers), and for long-term follow-up of repaired congenital defects.
• Pericardial disease — thickening, inflammation, and fluid around the heart (pericarditis, pericardial effusion, constrictive pericarditis).
• Cardiac masses and tumours — distinguishing between blood clot (thrombus), benign tumours (myxomas), and malignant tumours.
• Iron overload — T2* mapping quantifies iron deposition in the heart muscle, critical for patients with thalassaemia or haemochromatosis.

Common Heart Conditions Diagnosed by CMR

Cardiomyopathies

• Hypertrophic cardiomyopathy (HCM) — abnormal thickening of the heart muscle. Affects about 1 in 500 people. CMR measures wall thickness accurately and detects fibrosis (associated with arrhythmia risk). The most common cause of sudden cardiac death in young athletes.
• Dilated cardiomyopathy (DCM) — enlarged, weakened heart. CMR measures chamber size, function, and fibrosis pattern. Mid-wall fibrosis on LGE is associated with worse prognosis.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) — fatty/fibrous replacement of right ventricular muscle. CMR is part of the diagnostic criteria (Task Force criteria). Another cause of sudden death in young people.

Myocarditis

Inflammation of the heart muscle, often following a viral infection. CMR is the gold standard non-invasive test, using the updated Lake Louise Criteria (T2 mapping for oedema + LGE or T1 mapping for myocardial injury). Around 10-20 per 100,000 people per year are affected.

Ischaemic Heart Disease

CMR can detect previous heart attacks (even clinically silent ones), assess remaining viable muscle vs scar, and — with stress perfusion protocols (adenosine or regadenoson) — identify areas of the heart not getting enough blood during exercise (reversible ischaemia). Stress perfusion CMR is increasingly used as an alternative to nuclear perfusion scanning.

What to Expect During a Cardiac MRI

A cardiac MRI takes 45-60 minutes — longer than most other MRI scans because of the complexity of imaging a moving organ.

1. ECG leads — small sticky pads are placed on your chest to monitor your heart rhythm. The scanner uses your heartbeat to time the images (cardiac gating).
2. Positioning — you lie on your back. A cardiac coil (a flat pad) is placed over your chest.
3. Breath-holds — you will be asked to hold your breath for 10-15 seconds at a time during each image acquisition. This reduces movement artefact. Typically 15-25 breath-holds during the entire scan. Some newer techniques allow free-breathing acquisition.
4. Contrast injection — gadolinium is injected through a cannula partway through the scan. Images are taken before and after contrast to detect scarring (LGE). Some protocols also include adenosine infusion for stress perfusion assessment — this can cause a brief feeling of flushing, chest tightness, and breathlessness (normal and expected, lasting 2-3 minutes).
5. The scan — noisy as usual (knocking, buzzing). Headphones provided. The radiographer will talk you through each breath-hold via intercom.

Preparation

• You may need a recent kidney function blood test (eGFR) for contrast
• Avoid caffeine for 24 hours before if stress perfusion is planned (caffeine interferes with adenosine)
• Take your usual medications unless told otherwise
• Certain implants need checking — most modern pacemakers are MRI-conditional (safe under certain conditions), but older devices may not be

What Cardiac MRI Cannot Show

• Coronary artery anatomy in detail — coronary CT angiography (CTCA) or invasive coronary angiography are better for assessing coronary artery narrowing. CMR coronary imaging is possible but not yet standard practice.
• Arrhythmia mechanism — CMR shows structural substrates (scar, fibrosis) but cannot map the electrical pathway of an arrhythmia. Electrophysiology studies (EPS) are needed for that.
• Coronary calcium score — CT is the test for coronary calcium scoring.

Alternative Cardiac Tests

• Echocardiography (heart ultrasound) — first-line cardiac imaging. Quick, portable, no radiation. Good for assessing heart function, valve disease, and pericardial effusion. Less accurate than CMR for tissue characterisation, right ventricular assessment, and quantifying valve disease.
• CT coronary angiography (CTCA) — the best non-invasive test for coronary artery disease. Shows calcium score and coronary artery narrowing. Uses radiation.
• Nuclear perfusion scan (SPECT) — assesses blood flow to the heart muscle during stress. Being gradually replaced by stress CMR in many centres.
• Invasive coronary angiography — catheter-based, definitive assessment of coronary arteries with option for treatment (stent) at the same time.
• ECG and Holter monitor — for rhythm assessment. Do not show structural heart disease.

Treatment Pathways

• Cardiomyopathy — medication (beta-blockers, ACE inhibitors, anti-arrhythmics), lifestyle modification, ICD (implantable cardioverter-defibrillator) if high arrhythmia risk, heart transplant for end-stage disease.
• Myocarditis — rest from exercise (typically 3-6 months), monitoring, anti-inflammatory treatment. Most cases resolve fully. CMR follow-up to confirm resolution.
• Post-heart attack — medication (dual antiplatelet therapy, statins, beta-blockers, ACE inhibitors), cardiac rehabilitation, lifestyle changes. CMR viability assessment guides revascularisation decisions.
• Valve disease — monitoring, medication, valve repair or replacement surgery when criteria are met.

UK Statistics

• Cardiovascular disease causes around 160,000 deaths per year in the UK
• Around 7.6 million people in the UK live with heart or circulatory diseases
• HCM affects approximately 1 in 500 people
• Around 100,000 heart attacks occur in the UK each year
• Heart failure affects around 920,000 people in the UK

Frequently Asked Questions

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