Patients with chronic heart failure suffer from diminished leg blood flow (LBF). Question remains to what extent the distribution or the cardiac output (CO) is responsible. This study investigates whether CO and LBF could be measured reliably using phase contrast MRI during supine exercise. 10 healthy subjects performed a supine exercise test in the MRI at two days at different exercise intensities. Comparison between both days showed promising reproducibility of measuring CO and LBF during supine cycling in the MRI although LBF measurements proved more challenging.