Senik, M.R., M.N.A. Wahab, and M. Zamani. 2014. “The Study of Heart Rate Variability (HRV) Biofeedback through Zikir (Islamic Recitation) of High School Students”. Journal of Engineering and Technology (JET) 5 (1):31-38. https://jet.utem.edu.my/jet/article/view/125.