Heart rate (HR) variability is important with respect to disease prognosis and the effects of drugs. Lorenz scatterplots provide a simple way to evaluate HR variability visually. The relation of Lorenz scatterplots to frequency-domain HR variability was examined in 75 Holter recordings and in simulated HR trends. The length of Lorenz scatterplots was double-exponentially correlated with total frequency and very-low frequency powers, with correlation coefficients (r) of 0.88. The width of Lorenz scatterplots was highly correlated with the high frequency power (r=0.98). The sum of the width and length of Lorenz scatterplots was highly correlated with the total frequency power (r=0.92). Identical results were obtained when simulated HR trends were used. In conclusion, Lorenz scatterplots provide a simple way to estimate the frequency-domain HR variability.