BACKGROUND Energy drinks are frequently purported to improve cognitive function and concentration. However, the cardiovascular effects of these drinks have not been adequately studied. OBJECTIVE To determine the cardiac effects of a commercially available, multicomponent energy drink in healthy volunteers. METHODS Fifteen healthy adults were included in this prospective study. Individuals who had chronic medical conditions, were on chronic medication, or were pregnant or breast-feeding were excluded. Subjects abstained from caffeine for 48 hours prior to and during the study. In the morning on Day 1 of the study, while subjects were in a fasted state, baseline blood pressure (BP), heart rate (HR), and electrocardiographic (ECG) parameters were measured. Participants then consumed 500 mL (2 cans) of an energy drink and measurements were repeated 30 minutes, 1 hour, 2 hours, 3 hours, and 4 hours later. Participants then drank 500 mL of energy drink daily for the next 5 days. Day 1 protocol was repeated on Day 7. RESULTS On Days 1 and 7, maximum mean systolic BP (SBP), HR, and QTc interval occurred at 4 hours. Maximum diastolic BP (DBP) occurred at 2 hours on Days 1 and 7. Within 4 hours of energy drink consumption, on Days 1 and 7, respectively, SBP increased by 7.9% (p = 0.006) and 9.6% (p < 0.001), HR increased by 7.8% (p = 0.009) and 11.0% (p < 0.001), and QTc interval increased by 2.4% (p = 0.368) and 5.0% (p = 0.052). DBP increased by 7.0% (p = 0.046) and 7.8% (p = 0.063) within 2 hours of energy drink consumption on Days 1 and 7, respectively. CONCLUSIONS Although no significant ECG changes were observed, HR increased 5-7 beats/min and SBP increased 10 mm Hg after energy drink consumption.