This paper aimed to (a) validate a novel technique that quantifies the length of the trajectories the cardiac system follows within a two-dimensional state-space, and (b) test its usefulness to better understand how cognitive emotion regulation (CER) style is associated with cardiac output. A positive CER style was assessed in a sample of healthy adolescents (n = 57), and mean and total distances, in addition to heart rate variability (HRV) measures and cardiac entropy (SampEn), were calculated during a conflict discussion with the adolescents' mothers. Associations between distances and HRV measures in time and frequency-domains and SampEn were examined to better understand the physiological meaning of distances; further, whether a positive CER style would predict distances, HRV, and SampEn. Correlation analysis revealed that associations of distances with time-domain HRV measures were stronger than associations with frequency-domain HRV measures, while correlations between distances and SampEn were moderate. Hierarchical multiple regression analysis revealed that a positive CER style predicted distances and SampEn, but not HRV measures. Distances are clearly time-domain measures of HRV, but only partly capture the complexity of the heart signal. The results highlight the importance of assessing heart rate dynamics beyond HRV in the study of CER.