Cardiorespiratory coupling (CRC) accounts for the interactions between the heart period (HP) and respiration (RESP) and can be computed through the bivariate analysis of the HP and RESP time series. The study of CRC is useful to understand the chronic effects of different modalities of training on CRC regulation in athletes. Increases in CRC values have been associated with a raise of oxygen consumption. Several methods have been proposed to estimate the CRC, such as the squared coherence (K2). However, one of the main disadvantages of this approach is its inability to impose a directionality, thus limiting its ability in elucidating physiological mechanisms involved in chronic adaptation to exercise. We propose a tool able to account for causality, namely the causal K2, to estimate the CRC. Analysis was performed in 42 male healthy subjects (i.e., athletes and sedentary individuals), aged between 20 to 40 years old. Causal K2 was applied by considering the action of RESP on HP (K2RESP→HP), as well as of HP on RESP (K2HP→RESP). We found that athletes showed higher resting CRC (K2: 0.88 ± 0.11 versus 0.81 ± 0.13, p<0.05), and this increase is attributed to the temporal direction from RESP to HP (K2RESP→HP: 0.70 ± 0.16 versus 0.59 ± 0.19, p<0.05). We suggest the use of causality analysis when CRC is estimated, especially in trained individuals. Future studies should investigate the effects of different modalities of training on CRC and how the directionality is affected by different exercise protocols.