The time of day when cardiovascular events (e.g., acute myocardial infarction, stroke) are more likely to occur has been linked with the circadian rhythms of physiological variables that are responsible for cardiovascular regulation. Humans can be categorised into different circadian phenotypes (i.e., chronotype), dependent on their preferred time of sleep and wakefulness (i.e., early or late). An individual’s chronotype has been shown to influence circadian patterns of physical performance and body core temperature, and recently shown to influence the incidence of cardiovascular events. Specifically, early chronotypes are reported to be more susceptible in the morning while late chronotypes more susceptible in the evening. However, no studies to date have investigated the influence of chronotype on the circadian rhythms of physiological variables responsible for cardiovascular regulation. The aim of this study was to investigate whether different chronotypes display different circadian patterns for the critical physiological variables linked with cardiovascular events. In a repeated-measures experiment, 12 young, healthy participants (four early, four intermediate and four late chronotypes – determine via questionnaire) were tested between 08:00 and 10:00 h and again between 18:00 and 20:00 h. Baseline measurements of blood pressure, heart rate, cerebral blood flow velocity, ventilation and end-tidal partial pressure of carbon dioxide were measured in each session. Measurement of endothelial vascular function was obtained via flow-mediated dilatation (FMD) and four hypercapnic steps were used to assess ventilatory sensitivity and cerebral vascular reactivity (measured with transcranial Doppler). There was a significant interaction between chronotype group and time-of-day in FMD (p=0.002). Post-hoc analysis revealed that early chronotypes had a reduced FMD in the morning compared to the afternoon test (4.3±1.2 vs. 7.0±1.7%, respectively; p=0.028). In contrast, there were no significant differences in FMD between the morning and afternoon tests in intermediate chronotypes (2.7±0.6 vs. 2.6±0.4%, p=0.747), while the late chronotype group had an on average greater FMD response in the morning compared to the afternoon (5.8±1.7 vs. 3.0±1.3%, p=0.072). There were no significant time-of-day differences in cerebral vascular function, ventilatory sensitivity or baseline measurements among the different chronotype groups. These preliminary data indicate that the chronotype of an individual influences the circadian rhythm of cardiovascular function, with the most prominent difference seen in endothelial vascular function. These findings are consistent with the time-of-day rhythm in cardiovascular events and highlight potential mechanisms that may underpin this chronotype influence in the onset of these events.