Cardiovascular safety of marathon running in recreational runners remains unclear. We set up this study to comprehensively evaluate the effects of a marathon run on the profile of cardiovascular stress biomarkers in connection with transthoracic echocardiography. Thirty-three healthy male amateur runners, aged ≥50 years (mean age 57 ± 7) were enrolled. Venous blood samples were obtained before the marathon, just after the race, 2-4 and seven days after the marathon. Using novel single molecule counting technology we measured: plasma concentrations of high-sensitivity cardiac troponin I (hs-cTnI) and endothelin-1. N-terminal pro B-type natriuretic peptide was measured using electrochemiluminescence. Each participant had transthoracic echocardiography before and immediately after the race. We observed a sharp rise in the levels of all biomarkers after the race (all p < 0.01), which subsequently normalized after 2-4 days and stayed within normal range after seven days. Runners with intensive training programmes (>169 km/month, a median for the studied group) had lower hs-cTnI leak after the race (median 15.11 ng/ml and 31.2 ng/ml, respectively; p < 0.05). Neither transthoracic echocardiography measures of ventricles nor strain rates changed after the run. We observed a decrease in the left atrial volume index and increase in the maximal right atrial volumes (all p < 0.05). Changes in Doppler indices of diastolic function suggestive of alteration in left ventricular relaxation were observed. Marathon run is associated with sharp and significant rises in the biomarkers of cardiovascular stress. The profile of these changes, however, along with echocardiographic parameters, does not suggest irreversible myocardial damage.