The HeartMath institute is a research and education organization founded in 1991, dedicated to provide tools based on scientific research and evidence, to help people connect, perform optimally and enjoy life. The base of their 30+ years of research is the connection between the brain and the heart, and how the rhythm and pattern of our heartbeat actually sync with various emotional states, and can predict and influence our performance.

Over 300 Research publications can be found on their website:

https://www.heartmath.org/research/research-library/