Background: Enhanced left ventricular (LV) compliance is a common adaptation to endurance training. This adaptation may have differential effects under conditions of altered venous return. The purpose of this investigation was to assess the effect of cardiac (un)loading on right ventricular (RV) cavity dimensions and LV volumes in endurance athletes and normally active males. Methods: Eight endurance-trained (VO₂ max 65.4 ± 5.7 mL·kg^-1·min^-1) and eight normally active (VO₂ max 45.1 ± 6.0 mL·kg^-1·min^-1) males underwent assessments of the following: 1) VO₂max, 2) orthostatic tolerance, and 3) cardiac responses to lower body positive (LBPP) (0 to 60 mmHg) and negative (LBNP) pressures (0 to -80 mmHg) with echocardiography. Results: In response to LBNP, echocardiographic analysis revealed a similar decrease in RV end-diastolic cavity area in both groups (e.g. at -80mmHg normals: 21.4%, athletes: 20.8%) but a greater decrease in LV end-diastolic volume (LVEDV) in endurance athletes (e.g. at -80mmHg normals: 32.3%, athletes: 44.4%, p<0.05). Endurance athletes also had significantly greater decreases in LV stroke volume (LVSV) during LBNP. During LBPP, endurance athletes showed larger increases in LVEDV (e.g. at +60mmHg normals: 14.1%, athletes: 26.8%) and LVSV, despite similar responses in RV end diastolic cavity area (e.g. at +60mmHg normals: 18.2%, athletes: 24.2%, p<0.05). Conclusion: This investigation revealed that in response to cardiac (un)loading similar changes in RV cavity area occur in endurance-trained and normally active individuals despite a differential response in the LV. These differences may be the result of alterations in RV incluence on the LV and/or intrinsic ventricular compliance.