I'm sorry that you have been diagnosed with Supraventricular Tachycardia, or Paroxysmal Supraventricvular Tachycardia.
It is important that you do not do too much online reading on heart conditions because many times this will cause much more unnecessary grief, stress, and anxiety.
SVT is not a life threatening condition unless it is being caused by an underlying heart condition.
If you have an episode of PSVT, a technique called the Valsalva maneuver can be used to interrupt the fast heartbeat. Hold your breath and strain, as if you were trying to have a bowel movement, or cough while sitting with your upper body bent forward.
Splashing ice water on the face has been reported by some people as helpful.
Avoid smoking, caffeine, alcohol, and illicit drugs. Medications used to treat the disorder may be given as a preventive (prophylactic) treatment in people at a high risk or who have had previous episodes of PSVT.
Hope this helps you!