PITTSBURGH (KDKA) – They’re one of the most popular fitness trackers around, but a new study says your Fitbit might not be as accurate as you think.

A class-action lawsuit was filed earlier this year saying Fitbit trackers that measure your heart rate aren’t accurate.

The suit claims Fitbit trackers may be miscalculating users’ heart rates.

The study says heart rate monitors may be off by as much as “20-beats per minute” during high-intensity workouts.

For a healthy exercising adult, it’s not really an issue.

“For cardiac patients, we recommend that patients exercise in a heart rate target zone of 60 to 80 percent of their max heart rate,” said Dr. Amish Mehta, a cardiologist at AHN Jefferson Hospital.

“If we’re talking about someone who has a cardiac issue and they’re going out and this Fitbit is off by 20 beats a minute, they could be at risk for a cardiac event, even death,” said Matt Almendarez, an AHN exercise physiologist.

Dr. Mehta sees that possibility as rare though.

“There’s a slight possibility if someone is really trying to push themselves and hit a particular heart rate and the Fitbit telling them it’s lower than actually is and if they push themselves, they could have a negative outcome or an issue,” he says.

The technology is used in the more expensive models of the device, the Surge, Blaze and Charge HR.

The lawsuit was filed on behalf of people who bought these Fitbits specially to help them track their heart rate, whether for health reasons or to make sure they are getting the most out of their workouts.

Cal Poly Pomona was hired by attorneys for plaintiffs in a class-action lawsuit against the company.

Researchers at the Pomona school tested the heart rates of 43 adults using the PurePulse.

They then hooked the same individuals up to a medical device that measures heart rate.

But Fitbit responded to the study with a statement that reads in part:

“What the plaintiffs’ attorneys call a ‘study’ is biased, baseless, and nothing more than an attempt to extract a payout from Fitbit. It lacks scientific rigor and is the product of flawed methodology. Fitbit’s research team rigorously researched and developed PurePulse technology for three years prior to introducing it to market and continues to conduct extensive internal studies to test the features of our products.”

So, what should you do with your Fitbit.

“I would not tell someone not to use their Fitbit, but to be aware the accuracy of them might be something to be reconsidered,” said Dr. Mehta.

Dr. Katie Berlacher, a Cardiologist at UPMC joined the “KDKA Morning News” on Wednesday to talk about the Fitbit controversy.

“From a physician standpoint, I love when my patients are out exercising. If they wear a Fitbit, that’s great, if they want to bring in that information…and we can talk about it. I don’t think that any of us are making medical decisions based on Fitbit right now,” Dr. Berlacher said.

Dr. Berlacher added those that need to keep a close watch on their heart rate while exercising should do it, the old-fashioned way and learn how to use your fingers to check your pulse.

“Fitbits are great but, and the company will say this, they are not a medical device,” Dr. Berlacher said.