The present study examined the reproducibility of alterations in left ventricular function and cardiac biomarkers in a cohort of athletes following two marathons, one year apart. Eight participants in the 2004 and 2005 London Marathons were tested pre- and post-race via echocardiography and humoral analysis. Reductions in diastolic filling, unrelated to loading or heart rate, following both marathons were reproducible within individuals, which may be a function of exercise duration. In contrast, exercise-induced cardiac troponin release was inconsistent.