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We have recently proposed a novel CO index, namely pulse time reflection ratio (PTRR), which is extracted from photoplethysmogram and electrocardiogram and measurable from wearable devices, and proved that this index is potentially useful for dynamic CO monitoring in a preliminary study carried out on young, healthy subjects. In this study, we presented an evaluation of this technique against impedance cardiography on 64 subjects undergoing incremental maximal exercise testing, including 15 healthy elderly, 19 cardiovascular patients and 30 heart failure patients. Results showed significant intra-subject correlations (r) between PTRR and reference CO in all subjects (mean r: 0.93, p<;0.05) and no significant differences on mean r among subject populations (one-way ANOVA, p=0.48). With further development and testing on mobile subjects, this technique can be applied for long-term CO monitoring at home or in other dynamic situations.