Background: High-intensity interval training (HIIT) has gained interest as an effective alternative for the traditional moderate-intensity continuous training (MICT) to improve physical fitness and whole-body health, but its effect on the right ventricle (RV) is unknown. The aim of this thesis was to study the effects of HIIT and MICT on RV metabolism and function both in healthy men and in subjects with type 2 diabetes mellitus (T2DM) or prediabetes. 

Methods: In total, 28 healthy and untrained men and 26 untrained men and women with T2DM or prediabetes were randomized into HIIT and MICT groups. Subjects performed six supervised cycle ergometer sessions within two weeks (HIIT session: 4-6 x 30 s all-out cycling / 4 min recovery, MICT session: 40-60 min cycling at 60% VO2peak). RV glucose and free fatty acid uptake were studied by positron emission tomography. RV structure and function were determined by cardiac magnetic resonance. 
Results: In healthy men, both HIIT and MICT decreased RV glucose uptake while RV fatty acid uptake remained unchanged. Further, both exercise modes increased RV volumes and mildly decreased its ejection fraction. In diabetic subjects, RV glucose and free fatty acid uptake remained unaltered. Only MICT increased RV end-diastolic volume and RV mass, whereas both HIIT and MICT increased RV end-systolic volume and decreased RV ejection fraction. 

Conclusions: Two weeks of HIIT and MICT induce similar changes in RV of the healthy men regardless of markedly lower volume of HIIT. For a diabetic heart, MICT may be more beneficial as it improves RV dimensions more than HIIT.