If you are Canadian and a runner chances are you probably heard about this study that received media attention yesterday. The study used MRI data to find out what happens to the heart during a marathon.
The findings of the study suggest that less fit marathoners can damage their hearts during the marathon. This only seems logical to me as it takes months of training to properly train for a marathon. Jumping into a marathon without the proper training is a recipe for disaster.
Fortunately for runners who may have suffered heart damage from a marathon it is reversible over time.