Resonance Frequency Breathing appears to support emotional processes and improve heart rate variability.
This app helps you track your breathing pattern and keep it at around 6 breath/min, which is a common RF breathing rate.
Also, you can adjust the breathing rate to your taste.

Medical Disclaimer:
Please seek a doctor's advice in addition to using this app before making any medical decisions.
You should always seek the advice of your physician or another qualified health provider with any questions or concerns you may have regarding your health and you should never disregard or delay seeking medical advice because of information contained in or transmitted through this app.