It is hypothesized that a high level of normalized high-frequency (HFnu) component of HRV and a low standard deviation of normal-to-normal RR intervals (SDNN) could have a predictive value in terms of severity and mortality in critically ill patients suffering from COVID-19; furthermore, it is also hypothesized that these values might be related to the number of proinflammatory cytokines, such as IL-6, CRP, and procalcitonin. Here, CRP is linked to COVID-19.