Homeostatic control of cardiovascular function in response to, for instance, changes in blood volume or temperature is poor in REM sleep. There is considerable variability of heart rate and blood pressure according to fluctuations in the sympathetic–parasympathetic balance. This is primarily the result of erratic activity in the brainstem reticular formation. Overall, blood pressure is similar to that in wakefulness and the heart rate is greater than in NREM sleep. Cardiac output fluctuates according to the heart rate and blood pressure changes.

The coronary artery blood flow varies according to changes in blood pressure and heart rate. In general it is slightly greater than in NREM sleep, but the myocardial work is also increased.

Cerebral blood flow is similar to that in wakefulness, but greater than in NREM sleep, especially in the pons, thalamus and occipitotemporal cortex. As in NREM sleep it is coupled to central nervous system metabolic activity, and increases with hypercapnia.

The intracranial pressure rises particularly in REM sleep possibly due to increases in cerebral blood flow.

Renal blood flow is slightly reduced in REM sleep due to an increase in sympathetic activity, and this also underlies the reduction in skeletal muscle blood flow.

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