"People sometimes consume a number of these drinks one after the other. This situation can lead to a number of adverse conditions, including angina, cardiac arrhythmia (irregular heartbeat) and even sudden death," warned professor Milou-Daniel Drici from France. Speaking at the European Society of Cardiology (ESC) Congress, 2014, in Barcelona, Spain, he said that around 96 percent of these drinks contain caffeine, with a typical 0.25 litre holding as much as two espressos worth of caffeine.