Introduction. This study purposed to examine energy expenditure (EE) of one-hour hatha yoga (HY) practice and to compare changes in heart rate variability (HRV) during and right after HY practice. Material and methods. A total of ten experienced female HY practitioners participated in the study voluntarily. Daily EE on a weekday and during a one-hour HY session was measured using a metabolic holter. The ECG holter was applied to record HRV variables 5 minutes before, during, 5 minutes after and 10 minutes after the one-hour HY session. The HY session included HY asanas for the first 55 minutes and meditation during the last 5 minutes. Results. Participants showed 2201.40 kcal of total EE, and 421.70 kcal of active EE during the weekday. Active EE was 109.70 kcal (26% of daily active EE) during the one-hour HY session, and the mean MET was recorded as 2.57. HRV measurements showed crucial changes. Increased sympathetic activity observed in SDNN, RMSSD, NN50, pNN50, LF/HF, and HF did not reach the initial level after 15 minutes of total recovery time. Conclusions. One hour of HY practice provided moderate EE. Moreover, 10 minutes of supine rest in addition to 5 minutes of the meditation phase of HY practice is not seen as completely effective in improving parasympathetic activity and returning the practitioners to their initial level. Extending the meditation phase at the end of the HY session by more than 10 minutes and measuring the recovery process of HRV could add more detailed results to the literature.