Although popularity of ultra-long endurance races is growing, data on their consequences on cardiac function are still lacking. Thus, we aimed to assess the progressive cardiac consequences of the World's most challenging mountain ultra-marathon (Tor des Geants; Italy; 300km; 24000m D+).

Resting cardiac evaluations were conducted prior (pre-), during (mid-; km 150) and after (post-) the race on fifteen participants. Left and right ventricle (LV and RV) morphologies, functions and mechanics were assessed using standard tissue Doppler imaging and Speckle tracking echocardiography.

Runners completed the race in 126±15h. From pre- to post-, the increase in stroke volume (SV) (103±19 vs. 110±23 vs. 116±21mL; p<0.001 from pre- to post-race) was concomitant with the increase in LV early filling (i.e. peak E; 72.9±15.7 vs. 74.6±13.1 vs. 82.1±11.5cm.s-1; p<0.05). Heart cavity sizes were 12-19% higher at post-. Significant correlations were found between percent changes in peak E and LV end-diastolic volume (r=0.56, p<0.05) or left atrial and right ventricle diastolic areas (r=0.66, p<0.05; r=0.80, p<0.001; respectively). Resting heart rate and LV systolic strain rates demonstrated a biphasic adaptation since they were increased at mid- (55±8 vs. 72±11bpm, p<0.001) but returned to baseline pre- values at post- (55±8 vs. 59±8 bpm, respectively).

Whereas it is well-described that long duration exercise of several hours induces a transient LV dysfunction, we observed specific cardiac adaptations characterized by a progressive increase in SV and diastolic function during much longer exercise; e.g. 4-7 days of mountain running. Our data strongly support the key role of a cardiac volume overload in these alterations. The underlying mechanisms of such specific alterations after an extreme mountain ultra-marathon and their clinical implications remain challenging for the future.