I describe two simple breathing exercises that over a period of three months permanently cured not only my Supra Ventricular Tachycardia (SVTs) but also my Premature Ventricular Contractions. (PVCs are also known as ectopic beats or palpitations).
The idea for this breathing protocol came from the observation that the Valsalva Maneuver (holding breath and bearing down) will sometimes terminate an SVT while it is in progress.
So it seems that chest pressure and deep breathing affect the Vagus nerve. (The Vagus nerve has a central role in heartbeat regulation and the sympathetic/parasympathetic nervous system)
These exercises are not intended for use DURING an SVT episode. (Carefully watch the full video).
They in fact, over time, "trained" my heart to not present me with SVTs in the first place.
(The exercises are simply done during the course of your normal day. There is no need to "put aside" extra time to do them).

This is not medical advice, it is an account of my own personal SVT experience.