What are the risks if i don't treat supraventricular tachycardia?

Depends on the type: There are many types of supraventricular tachycardia. Among the different types; effects & frequency vary among persons. For example, for a very limited av nodal reentrant tachycardia once or twice a year that does not last long and does not go fast, the effects are usually benign. However, if the heart goes very fast you could pass out. Atrial fibrillation of any rate increases stroke risk.

It depends: Some svt are benign and self limited and if untreated you may jug feel uncomfortable (palpitations, dizziness). Some are more dangerous and longer lasting and could lead to syncope (passing out) and in very rare cases to death.

SVT: As we get older, the risks of a heart attack (myocardial infarction) increase, from the demand that SVT may place on an aging heart. In an otherwise healthy heart, the risk of dying from SVT is present, but very low. Untreated SVT can lead to acute heart failure symptoms during the episodes. SVT episodes that persist more than a couple days, can lead to weakening of the heart muscle.

Varies: If you have no symptoms, there are no risks. The treatment of svt is for symptomatic relief. (atrial fibrillation patients: this does not apply to you - in af, the rate must be controlled and some people need anticoagulation.).