To orient yourself for what we refer to as a "short axis stack", imagine, if you will, chopping a fat gherkin into slices. This is a sequence of six MRI 'slices' through a man's heart, from the top through to the bottom. He had suffered a large heart attack (infarct) a few weeks earlier, where the artery supplying the front of the heart blocked and the heart muscle was irreversibly damaged. It's unusual to actually be able to see the scar tissue so clearly, but the white part of the muscle which isn't thickening is essentially dead heart. You can see a large portion of the wall is not contracting like the opposite side. A serious complication of a large heart attack like this is a blood clot forming in the part of the heart that isn't moving properly. You can see a ball-shaped clot (thrombus) at the bottom of the heart. Normally these don't move but this one looks less stable than most and it might dislodge and cause a stroke (blood clot in the brain). Therefore this man was started on warfarin, a drug that reduces the blood's ability to clot.