By the means of spectral analysis, dependency of heart rate variability (HRV) on average R--R-intervals (R--Rav, sec) is explored at controlled (forced) breathing. According to our findings, the dependency of the peak frequency at a spectral density graph for source series of R--R-intervals upon the RRav may be presented by the following formula: fp 1.0 = fr: RRav, where fp 1.0--peak frequency when R--Rav = 1.0 sec, fp--peak frequency at current R--Rav. For correcting (standardization) the frequency domain borders of spectral power (fd) of sources series of the R--Rav-intervals it is possible to use the formula: fd = fd 1.0 R--Rav, where fd 1.0--frequency domain border at R--Rav = 1.0 sec. The correction (standardization) of frequency domain borders of spectral power (fd), frequency peaks (fp 1.0) of sources series of the R--Rav-intervals as compared to current R--Rav allows to compare different series of the R--Rav-intervals without using the transformation to the discrete event series (DES).