Marcy and Jack go back to nineteen ninety six, the origin paper for cardiac coherence — twenty volunteers, five minutes of genuine appreciation, and a heart rhythm that pulled breathing and blood pressure into the same ten second wave — plus the two minute Freeze-Frame practice it was built on. Read the paper: Cardiac Coherence: A New, Noninvasive Measure of Autonomic Nervous System Order (William A. Tiller, Rollin McCraty, Mike Atkinson, 1996, Alternative Therapies in Health and Medicine) — https://www.heartmath.org/assets/uploads/site/file/pdf/c/cardiac-coherence.pdf