You are right, the Val salva maneuver is used when someone is in SVT. It's the 'first line of attack' when treating someone with the condition. Of course you should have them on a cardiac monitor while they do it. The joke amongst medical people is 'If you don't poo yourself doing it, then you aren't doing it properly' If that doesn't work then you try medication (Adenosine), and when that doesn't work, you sedate them and give them a shock across the heart (a lower power than when you are shocking the heart in a cardiac arrest)