The high levels of caffeine in energy drinks may lead to cardiac complications, suggests a case report. The case, reported in the Journal of Addiction Medicine, the official journal of the American Society of Addiction Medicine (ASAM), adds to previous reports of adverse cardiovascular events related to consuming energy drinks, including abnormal heart rhythms (arrhythmias) or improper beating of the heart, whether irregular, too fast or too slow. The patient was a 28-year-old man seen in the emergency department after developing vomiting with blood. On examination, the only abnormality (other than obesity) was a very fast heart rate - about 130 beats per minute. An electrocardiogram revealed an abnormal heart rhythm called atrial fibrillation: a common type of arrhythmia that can lead to serious complications if sustained. Further tests showed no other heart problems. The patient said he routinely drank two cans of energy drinks per day - for a total caffeine content of 320 milligrams - along with two or three beers. No other common causes of his heart rhythm abnormality were apparent. With medications, the atrial fibrillation resolved over 48 hours. Endoscopy showed a tear of the stomach and esophagus, probably caused by forceful vomiting. The patient was sent home in stable condition. At one year's follow-up, he had no further symptoms of arrhythmia. Although several factors might have contributed to the patient's atrial fibrillation, the researchers said, "We believe that energy drink consumption played a key role." Maryam Sattari of University of Florida, Gainesville is the lead author of the report. A review of the medical research identified at least eight cases of cardiovascular events linked to energy drinks. The researchers discussed several mechanisms by which the high caffeine content of these products might lead to cardiovascular events. These include other ingredients, such as taurine, that might heighten the effects of caffeine; using energy drinks along with alcohol or illicit drugs; or high stress levels. Energy drinks have become increasingly popular in recent years, especially among adolescents and young adults. Marketed as "nutritional supplements," these beverages are not subject to the caffeine limits on soft drinks, or to the safety testing and labeling required for medications. "We suggest that arrhythmia could be a complication of energy drink consumption," Sattari and coauthors wrote.