[Skip to content]

Royal Brompton & Harefield NHS Foundation Trust
For patients & carers
Search our Site
A nurse smiling

Conditions and treatments 

Cardiovascular magnetic resonance (CMR) scan

A CMR scan uses a strong magnetic field and radio waves to create detailed images of your heart. It gives us information on the structure of your heart and blood vessels and how well they are working.

What happens during a CMR scan?

We will ask you to lie on a bed that will slide into the scanner. 

During the scan, an electrocardiogram (ECG) will help us to make sure we take the pictures at the right time during your heart beat. It involves placing electrodes (small sticky patches) on your chest. 

The electrodes are connected by leads to a monitor that records the rhythm and electrical activity of your heart. A small monitor on your chest will receive the radio signal that creates the image of your heart. This is not painful.


We will ask you to lie as still as possible and to hold your breath for a few seconds while we take the scan. This stops your chest from moving and ensures that the images we take are as clear as possible.


Sometimes we need to get extra information from the scan by using a contrast agent. This is a colourless fluid that we can inject into a vein in your arm and lets us see your heart and blood vessels more clearly. We will let you know before the scan if we need to use a contrast agent.

Can anyone have a CMR scan?

Patients with certain kinds of metallic implants, or any other metal in their body, sometimes cannot have the scan. This is because the scanner uses a very strong magnet, which attracts certain metals.


Please let us know before your appointment if you have:

  • a pacemaker

  • implants or metal in your body, such as a stent

  • small pieces of metal in your eye (e.g. from welding)  

  • problems with your kidneys or are on kidney dialysis

  • had any major surgery or illness


It is important that you let us know if you are, or think you may be, pregnant, as it may be better to wait until after your child is born to have the scan. This can help ensure your well-being and that of your baby.

For more information about your CMR scan, please download the patient information leaflet below. It includes information on how to prepare for your scan as well as possible risks and side effects.

Royal Brompton

Sydney Street,
London SW3 6NP
Tel: +44 (0)20 7352 8121