"A 2007 article in the UK's "Daily Mail" shows that the very high caffeine content of energy drinks, as well as a chemical called taurine, caused a spike of between 8 and 11 percent of the resting heart rate and blood pressure of study participants after drinking two energy drinks each day for a full week."
Read more: http://www.livestrong.com/article/132422-what-speeds-up-your-heart-rate/#ixzz2CFPHiK29
I really never drunk energy for this simple fact my friends told me a several years back before energy drinks got really popular. The can cause heart arrhythmia.
" An arrhythmia (ah-RITH-me-ah) is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.
A heartbeat that is too fast is called tachycardia (TAK-ih-KAR-de-ah). A heartbeat that is too slow is called bradycardia (bray-de-KAR-de-ah).
Most arrhythmias are harmless, but some can be serious or even life threatening. During an arrhythmia, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs."