Magnetic resonance imaging (MRI) is a highly sophisticated technique with numerous medical applications, however only recently has it proved especially useful for investigating cardiac problems. Unlike conventional X-rays, CT scans and coronary angiograms, there is no radiation involved in the process; instead MRI uses a very powerful magnetic field to produce images of the heart. CMR can evaluate multiple aspects of the heart, including structure, function and blood supply to the heart.

During the scan the patient will lie on a moveable examination table, which then slides inside the scanner. The scanner tube is longer and narrower than a CT scanner but it is well lit and open at each end to help minimise any claustrophobia. As the images are acquired the scanner makes a loud knocking noise and headphones with music are provided to minimise this. The scan takes around 45 minutes, during which the patient will need to lie still. Some imaging sequences require breath holds for about 10 seconds whilst images are being taken, and for some scans an injection of a substance called gadolinium is required which, unlike many other contrast agents, does not contain iodine, which some people are allergic to. If the blood supply to the heart is also being assessed (a perfusion scan) an infusion of a drug such as adenosine will be administered to speed up the heart and simulate stress. The infusion may cause some chest tightness and flushing, but this is perfectly normal and only lasts about 3 minutes. The patient will be told when to expect this during the scan.

After the scan the patient is free to return to their normal daily activities immediately.