Sugar highs have been debunked time and time again. I’ll reiterate what the other poster said. If you experience any negative symptoms from a sweet dessert you really should see a doctor.

A normal healthy body produces enough insulin that unless you’re eating insane amounts of pure sugar (I’m talking pounds of raw sugar kind of insane) your blood sugar levels will stay on a very narrow band and your heart should not race.

How high are you talking here?

A little bump isn’t anything unusual, it’s the blood sugar spiking, then hormones kicking in as the cycle adjusts. But that’s not what I’d call “racing”. Hell, it very often isn’t even an actual increase to pulse as much as it is an awareness of one’s heartbeat.

But if you’re jumping up more than, say, ten beats a minute for more than maybe five minutes, bring it up to your doctor, make sure everything is fine. Could just be that we have different usages of racing, but if that’s not the case, it can be a sign of something out of whack. What I’ve run into with my patients back in the day was either incipient diabetes, or the early stages of heart disease. But, again, that’s if the spike in pulse is more than maybe ten extra a minute, or lasts longer than what a jump scare can cause

It’s one of those things where if it is a sign of something starting to get wonky, starting is the key word. Treating things early means treatment is easier and has higher success rates, sooner.