Very slow yogic breathing techniques provide valuable insights into mechanisms of autonomous nervous system regulation that are usually not available for human subjects. This paper presents results of eight sessions of Nadi Shodhana Pranayama practiced at rate of one breath per minute. We characterized statistic and spectral measures of heart rate variability before, during, and after exercises. Significant changes include increase of VLF frequencies caused by slow breathing and decrease in average interbeat interval from 959.3 to 904.1 ms (t(7) = -7.5, p<0.001). We present the results of HRV analysis and analyze origins of characteristic frequency components. The most prominent changes of the exercise include significant increase of respiratory sinus arrhythmia (RSA) and LF/HF ratio, and decrease of breathing frequency after the exercise against the state before the exercise. The maximum LF frequency decreased from 0.0919 Hz to 0.07125 Hz (t(7) = -3.255, p < 0.01), indicating the decrease of average breathing rhythm from 5.5 breaths/min to 4.3 breaths/min. In addition, the state after the exercise is characterized by disappearance of VLF frequencies from the spectrum, and a significant increase of LF/HF from 14.33 to 50.93 (t(7) = 2.461, p <.05).