The effects of propranolol on the heart rate variability was studied in anesthetized outbred male rats, to which the drug was administered as intracisternal and intraperitoneal injections. Propranolol was found to increase the power of low- and high-frequency components of the heart rate. In influencing the heart rate variability, propranolol has the central mode of action. It is suggested that the ability of propranolol to increase the power of the low and high frequency components of the heart rate is related to its enhancing effect on the central cardiac vagal control.