"Athlete's heart" is characterized by an increase in ventricular chamber sizes 
and myocardial mass (MM), and is mainly observed in endurance athletes. At 
present, it remains unclear whether cardiac adaptations in long-distance runners 
differ from those in triathletes. Twenty male triathletes (mean age 38.7 ± 6.2 
years) and 20 male marathon runners (mean age 44.1 ± 7.9) underwent cardiac 
magnetic resonance imaging to calculate left and right ventricular end-diastolic 
volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction 
(EF), and MM. Late-enhancement (LE) imaging was used to exclude structural 
alterations or myocardial scarring. EDV, ESV, SV, and EF for the left and right 
ventricles, as well as MM, did not differ between long-distance runners and 
triathletes, although the weekly training volume was significantly higher in 
triathletes (17.05 vs 9.95 h/week, P < 0.0001). There was a significant 
correlation between weekly training volume and right and left EDV, right and 
left ESV as well as MM within the study group. Myocardial LE was absent in all 
athletes. Highly trained male long-distance runners and triathletes have 
comparable cardiac parameters. However, the extent of physical training seems to 
be associated with the degree of cardiac adaptation in endurance athletes. The 
absence of LE supports the idea that athlete's heart is a nonpathological 
adaptation of the cardiovascular system.