Energy drinks might be a quick way of getting an extra boost of energy, but how is it affecting your heart? According to a new study presented at the Radiological Society of North America’s annual meeting, energy drinks can make the heart contract rapidly.

In the study, 18 healthy volunteers drank an energy drink that contained 400mg of taurine and 32mg of caffeine per 100ml (about 3,4 ounces). MRIs of heart function showed a 6% increase in heart contraction rate after consuming an energy drink, when performed an hour before and an hour after the study participants consumed the drink. Researchers suggest that the change in heart function was due to the blend of taurine, sugar and caffeine. In a second experiment, with drink only containing caffeine, no significant increase in heart contractions were found. Read these 9 New NRG Drink Facts.

Co-author Jonas Doerner from the University of Bonn advises children and those with irregular heart beats to avoid energy drinks until more studies are conducted, although the long-term effects of consuming energy drinks are not known. Authors of the study note that the findings are preliminary and subject to change until published in a peer-reviewed journal.