Previous studies have revealed that during a race, marathon runners often show evidence of dangerous changes to the heart, including
an enlarged right atrium (the chamber that receives oxygen - starved blood from the body) and elevated levels in the blood of enzymes that signal heart damage.
In a similar fashion to the changes to the left
atrium with certain left - sided heart diseases, diseases that primarily affect the
right side of the heart (e.g. primary pulmonary hypertension, heartworm disease, tricuspid valve dysplasia, pulmonic stenosis) may reduce forward flow of blood into the pulmonary circulation and, again depending on severity, may lead to a build - up of volume and / or pressure within the
right atrium which will also try to
enlarge to compensate.