Whats the fastest your heart rate can be during svt?

Depends. Supraventricular tachycardia often has abrupt rate changes often with the rate higher than sinus tachycardia - infants > 220 bpm - children > 180 bpm - adults > 160 bpm.
Svt rate. it depends on the age, it can usually go up to around 300 beats per minute, but most are slower.

Related Questions

I have svt, I usually get episodes once a month (fast heart rate)but everytime im pregnant, nothing happens, then after birth it come back again. Why?

SVT. Pregnancy changes your hormonal state and other hemodynamic related parts of your physiology. There are multiple possible reasons for the improvement with pregnancy. We generally don't recommend staying pregnant however as a treatment for svt. Read more...