Human cardiovascular control is automatic. Increases and decreases in heart rate and blood pressure function through negative feedback loops, with exercise, posture, stress, etc. as inputs, and signals from the autonomic (automatic) nervous system as outputs. Changes in heart rate and blood pressure are not random, and under normal resting conditions oscillations are apparent at frequencies corresponding to the respiratory rate, and at frequencies lower than respiration. These oscillations in naturally-occurring autonomic rhythms can be interpreted in the frequency domain using power spectral analysis. In this presentation, I will present original data from 3 recent 9-month missions aboard the Russia Space Station "Mir" to show how expression of the variance of heart rate and blood pressure as a function of frequency (using fast-Fourier based power spectral analysis) lends insight into the effects of microgravity on human cardiovascular control. I will discuss pitfalls and limitations of frequency-domain assessments in the hopes of fostering a collaborative spirit between physicists and physiologists.