Energy drinks are known to boost stamina, but consuming these beverages could also lead to a number of heart problems.

Researchers found that energy drinks -- popular in dance clubs and during physical exercise -- can lead to a number of adverse conditions including angina, cardiac arrhythmia (irregular heartbeat) and even sudden death. Nearly 96 percent of these beverages contain caffeine, with a typical 0.25 liter can holding 2 espressos worth of caffeine.

"Caffeine is one of the most potent agonists of the ryanodine receptors and leads to a massive release of calcium within cardiac cells," researcher Milou-Daniel Drici said in a statement. "This can cause arrhythmias, but also has effects on the heart's abilities to contract and to use oxygen."

For the study, researchers analyzed adverse events reported to the agency between Jan. 1, 2009 and Nov. 30, 2012. The findings were compared to published data in the scientific literature.

The researchers found that consumption of the 103 energy drinks in France increased by 30% between 2009 and 2011 up to over 30 million liters. The leading brand made up 40% of energy drinks consumed. Two-thirds of drinks were consumed away from home.

During the two year period 257 cases were reported to the agency, of which 212 provided sufficient information for food and drug safety evaluation. The experts found that 95 of the reported adverse events had cardiovascular symptoms, 74 psychiatric, and 57 neurological, sometimes overlapping. Cardiac arrests and sudden or unexplained deaths occurred at least in 8 cases, while 46 people had heart rhythm disorders, 13 had angina and 3 had hypertension.

"We found that 'caffeine syndrome' was the most common problem, occurring in 60 people," Drici said.

The syndrome is characterized by a fast heart rate (called tachycardia), tremor, anxiety and headache.

"The general public need to know that so-called 'energy drinks' have absolutely no place during or after physical exercise, as compared with other drinks designed for that purpose," Drici added. "When used in long alcoholic cocktails, the caffeine in 'energy drinks' enables young people in dance clubs or elsewhere to overcome the unwanted effects of alcohol, leading to an even greater intake of caffeine."

Drici concluded that doctors should warn patients with cardiac conditions about the potential dangers of these drinks and ask young people in particular whether they consume such drinks on a regular basis or through binge drinking.

The findings were recently presented at ESC Congress 2014.