What Does a Cardiac MRI Show and How Long Does It Take?

The short answer: A cardiac MRI shows the size and pumping strength of your heart chambers, your valves and large vessels, and any scar or inflammation in the heart muscle. Per MedlinePlus, the test most often lasts 30 to 60 minutes but may take longer. Stress scans and check-in add time.

What does a cardiac MRI show?

A cardiac MRI uses a strong magnet, radio waves, and a computer to make moving pictures of the heart. It uses no radiation. The National Heart, Lung, and Blood Institute says it gives "an accurate look at the heart muscle, heart chamber sizes and function, and connecting blood vessels."

A full exam is built from several image types. Each one answers a different question:

• Function (cine images): short movies of the beating heart. They measure chamber volumes, wall thickness, heart muscle mass, and ejection fraction (the share of blood pumped out with each beat). The 2020 SCMR position paper on clinical indications calls cardiac MRI the widely accepted noninvasive gold standard for these measurements.
• Scar (late gadolinium enhancement, or LGE): pictures taken after contrast dye. Damaged or scarred muscle holds the dye longer and shows up bright. This is how the scan finds old heart attacks and some cardiomyopathies.
• Tissue maps (T1, T2, and T2* mapping): color-coded measurements of the muscle itself. T2 images show swelling and inflammation. T2* mapping measures iron buildup in people who get many blood transfusions.
• Blood supply (perfusion): a first pass of dye through the muscle, often under drug-induced stress, to find areas that do not get enough blood.
• Blood flow: phase-contrast images measure how much blood moves through valves and vessels, which helps grade leaky or narrow valves.

MedlinePlus lists the conditions it is used to evaluate. These include damage after a heart attack, heart defects present from birth, tumors, weak heart muscle, heart failure symptoms, and valve disease. Abnormal results can point to myocarditis (heart muscle inflammation) or fluid around the heart. The SCMR panel rates cardiac MRI as a top-class indication for many cardiomyopathies, including hypertrophic cardiomyopathy, cardiac amyloidosis, sarcoidosis, and myocarditis.

How long does a cardiac MRI take?

MedlinePlus says a heart MRI "most often lasts 30 to 60 minutes but may take longer." That is time on the table. Your visit is longer because of check-in, the safety screening form, changing, and the IV.

Three things stretch a scan:

• Contrast and scar images. The SCMR 2020 standardized protocols call for a wait of at least 10 minutes after the dye before scar images. The team uses that gap for other pictures, but it sets a floor.
• Stress testing. A stress scan takes two sets of blood-supply pictures. SCMR asks for at least 10 minutes between the stress and rest dye doses.
• Breath-holds and heart rhythm. An irregular heartbeat or trouble holding your breath can mean repeat images.

Our guide to how long an MRI takes compares cardiac exams with other body parts. Ask your imaging center for its own estimate, since protocols differ by question and by site.

What happens during a cardiac MRI, step by step?

This timeline follows the order in the SCMR protocols and the patient steps described by MedlinePlus, NHLBI, and RadiologyInfo.org. Your center may change the order.

1. Arrival and screening. You fill out a metal and implant form, remove jewelry, and change into a gown. Tell staff about a pacemaker, defibrillator, or any implant.
2. IV placement. A nurse or technologist places an IV in your hand or forearm for the contrast dye. A stress scan with adenosine often uses two IVs, one in each arm.
3. ECG leads. Stickers go on your chest. NHLBI explains that an electrocardiogram tracks your heart rhythm, and "your pictures will be coordinated with your heart beat."
4. Positioning. You lie on your back. A padded coil rests on your chest to pick up the signal. You get earplugs or headphones, because the scanner is loud.
5. Scout and function images. The first pictures locate the heart. Then come the cine movies. For each set, the technologist asks you to hold your breath for a few seconds. NHLBI notes this happens "multiple times during the test."
6. Contrast injection. If your exam uses dye, it goes in through the IV. Some cardiac MRIs do not need contrast at all.
7. Scar images. After the 10-minute minimum wait, the late gadolinium enhancement pictures are taken, again with breath-holds.
8. After the scan. The IV comes out. MedlinePlus says there is no recovery time unless you had sedation. If you were sedated, someone must drive you home.

Our MRI with contrast guide explains how gadolinium dye works and who needs kidney checks.

What changes if you have a stress cardiac MRI?

A stress cardiac MRI checks blood flow to the heart muscle when the heart works harder. MedlinePlus says these tests are "mostly used for very serious heart problems." Most centers use a drug instead of a treadmill. SCMR notes that vasodilator stress is more common than stress with dobutamine.

• The drug. Adenosine runs as an infusion for 2 to 4 minutes, per SCMR. Regadenoson is a single injection. Dye goes in about 45 to 60 seconds after regadenoson.
• How it feels. SCMR lists flushing, chest pain, palpitations, and breathlessness as possible effects. Staff watch your heart rate and blood pressure the whole time.
• Two sets of pictures. Stress pictures come first, then rest pictures at least 10 minutes later.
• Monitoring after. MedlinePlus says you are watched for 10 to 15 minutes after any stress test, or until your heart rate returns to normal.

How should you prepare for a cardiac MRI?

Preparation is simple for a standard scan. A stress scan has extra rules.

• Food and drink. MedlinePlus says you may be asked not to eat or drink for 4 to 6 hours. RadiologyInfo notes that rules vary between facilities. SCMR explains that fasting is often advised for stress scans because the drugs can cause nausea.
• Caffeine. For a stress scan, SCMR advises avoiding caffeine for 12 to 24 hours. That includes coffee, tea, chocolate, and caffeinated medicines, because they blunt the stress drug.
• Medicines. RadiologyInfo says to take your regular medicines as usual unless told otherwise. Ask about beta-blockers and nitrates if you are having a dobutamine stress test.
• Devices. Bring your device card. Many pacemakers and defibrillators can be scanned under a set protocol (see our pacemaker and defibrillator guide).
• Claustrophobia. Ask your doctor about a mild sedative ahead of time, and arrange a ride home if you take one.

If your scan is checking for heart strain from long-term high blood pressure, hypertension.md covers blood pressure targets and home readings.

Is a cardiac MRI safe?

For most people, yes. RadiologyInfo.org says the exam "poses almost no risk to the average patient" when safety rules are followed. There is no radiation. The main risks come from metal objects and implants in the strong magnetic field.

Gadolinium contrast is very safe for most people, per MedlinePlus. Allergic reactions are rare. RadiologyInfo notes that a rare condition called nephrogenic systemic fibrosis is linked to gadolinium in people with serious kidney disease, and is exceptionally rare with newer agents. Very small amounts of gadolinium can stay in the body, with no known health effects.

The bottom line

A cardiac MRI measures how well your heart pumps, maps scar and inflammation in the muscle, and can test blood supply under stress. Plan for 30 to 60 minutes in the scanner, and longer for a stress scan. Expect ECG stickers, an IV, and many short breath-holds. Ask your center about caffeine and fasting rules ahead of time.

Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your cardiologist or imaging center about the protocol and preparation for your scan.