Each MRI may last up to 1 hour. An MRI obtains body pictures created by using magnetic energy rather than x-ray energy. To have the scan, you will lie on a table that slides into the scanner, which is like a large tube. An MRI examination of your heart will be done to assess heart function. You will be asked to lie still and follow simple breathing instructions during the procedure. The MRI data will be processed to evaluate the volume of blood being pumped by your heart, a value that may be useful in describing heart function.