Energy drinks may get your heart pumping in the wrong way, a new study suggests.

The study, which observed the effects of energy drinks in 18 people, found that those who drank high levels of caffeine or taurine showed significantly increased heart contraction rates one hour later.

"Until now, we haven't known exactly what effect these energy drinks have on the function of the heart," study researcher Jonas Dörner, of the cardiovascular imaging section at the University of Bonn, Germany, said in a statement. "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, which was presented on Monday at the annual meeting of the Radiological Society of North America, used MRI scans in 18 healthy volunteers -- 15 men and three women with an average age of 27.5-- to see how the chemicals in energy drinks affected their hearts. Each participant drank a mixture containing taurine and caffeine. An hour after consuming the drinks, cardiac MRIs of the participants showed significantly increased peak strain and peak systolic strain rates in the left ventricle of their hearts.

"Usually energy drinks contain taurine and caffeine as their main pharmacological ingredients," Dörner said. "The amount of caffeine is up to three times higher than in other caffeinated beverages like coffee or cola.”

This isn’t the first study to address the harmful effects energy drinks pose. A 2013 report from the Substance Abuse and Mental Health Services Administration stated that in the U.S. from 2007 to 2011, the number of emergency department visits related to energy drink consumption nearly doubled, increasing from 10,068 to 20,783.

The American Beverage Association, which represents energy drinks, says the study is incomplete.

"The fact remains that most mainstream energy drinks contain only about half the caffeine of a similar size cup of coffeehouse coffee," the industry group said in a statement. "Caffeine is a safe ingredient and is consumed every day in a wide variety of foods and beverages, including energy drinks which have been enjoyed safely by millions of people for nearly three decades. Also, this paper, which looks at only 18 adults, has not been peer-reviewed or published."

The study, which is ongoing, has only shown the short-term effects of energy drink consumption.

"We have shown that even small amounts of energy drinks alters heart function,” Dörner told HealthDay. "Because of that, further investigation needs to be done to address concerns regarding long-term effects on kids and long-term effects on people with heart disease."