Heart rate variability changes during yoga

Telles, S., Singh, N., & Balkrishna, A. (2011). Heart rate variability changes during high frequency yoga breathing and breath awareness. Biopsychosocial Medicine, 5(4), doi: 10.1186/1751-0759-5-4.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3088536/