Atrial fibrillation is a heart rhythm disorder that affects millions of people. It can lead to potentially disabling or deadly strokes. Researchers from Johns Hopkins University School of Medicine adding motion-tracking software to standard MRI heart scans of 149 men and women with atrial fibrillation. The scans revealed specific changes in the muscles of the left atrium that increased stroke risk in some of the volunteers. These changes were not associated with age or other risk factors for stroke. This could help many people with this condition to avoid taking warfarin or other clot-preventing medications for life. But it is much too early to include MRI as part of the standard evaluation of people with atrial fibrillation — not to mention that such scans would significantly increase the cost of these evaluations. For now, doctors will continue to use standard tools to help determine stroke risk.