The participants to the challenge are required to characterize cardiorespiratory interactions from the spontaneous fluctuations of heart period and respiratory flow during spontaneous breathing and controlled respiration at different respiratory rates in healthy subjects. The aim is to gain insight on the dependance of cardiorespiratory coupling on the breathing rate. Characterization could be carried out in any domain (i.e., time, frequency, and information domain) using any tool or metric that it is deemed to be helpful in assessing cardiorespiratory control and its evolution with the breathing rate.