Energy drinks loaded with caffeine intensify heart contractions and alter the way that the heart beats, researchers have warned.
A team from the German University of Bonn tracked the heartbeats of 17 people one hour after they consumed an energy drink.
The study revealed that heart contractions were more forceful after the energy drink.
Researcher Dr Jonas Dorner said: "Until now, we haven't known exactly what effect these energy drinks have on the function of the heart.
"The amount of caffeine is up to three times higher than in other caffeinated beverages like coffee or cola.
"There are many side-effects known to be associated with a high intake of caffeine, including rapid heart rate, palpitations, rise in blood pressure and, in the most severe cases, seizures or sudden death."
The research team supplied the study participants with a drink containing 32mg per 100ml of caffeine and 400mg per 100ml of taurine.
The report indicated that the left ventricle, the chamber of the heart that pumps bloody around the body, was contracting more per hour after the energy drink was consumed.
Dr Dorner continued: "We've shown that energy drink consumption has a short-term impact on cardiac contractility.
"We don't know exactly how or if this greater contractility of the heart impacts daily activities or athletic performance."
Dr Dorner warned that caffeine energy drinks should be avoided by children and people with an irregular heartbeat (cardiac arrhythmias).
"There are concerns about the products' potential adverse side effects on heart function, especially in adolescents and young adults, but there is little or no regulation of energy drink sales."
The study was presented at a meeting of the Radiological Society of North America (RSNA) in Chicago.