Extracellular contrast agents such as gadolinium can also be used to characterize myocardial viability, as myocardial perfusion correlates with function. When gadolinium is first injected into the systemic venous circulation, the contrast agent will appear bright in the MR image as it perfuses throughout ventricles and into the myocardium. This enhancement will occur within a few heartbeats. Contrast agents have altered T1 and T2 relaxation times in comparison to blood and thus appear brighter in the image. The regional myocardial distribution in the contrast enhancement can be used to determine the uniformity of perfusion, as well as the rate. Regions in the image which appear dim may suffer from an obstruction in the microvasculature, or indicate an occluded coronary artery.

Delayed contrast enhancement using gadolinium is the preferred method to identify a scarred region caused by a chronic myocardial infarction. Signal enhancement in scarred regions will occur approximately 5 minutes after the initial contrast bolus. Scarred regions will retain the contrast agent as cell death and tissue edema (which occur after an infarction and subsequent scarring) alter the wash-in and wash-out kinetics of the extracellular contrast agent.