Although coffee is a widely used, pharmacologically active beverage, its impact on the cardiovascular system in controversial. To explore the effects of acute caffeine ingestion on brachial artery flow-mediated dilation (FMD) in subjects without coronary artery disease (CAD; controls) and patients with CAD, these authors prospectively assessed brachial artery FMD in 40 controls and 40 age- and gender-matched patients with documented stable CAD on 2 separate mornings 1 week to 2 weeks apart. After overnight fasting, discontinuation of all medications for > 12 hours, and absence of caffeine for >48 hours, participants received capsules with 200 mg caffeine or placebo. One hour after drug ingestion, patients underwent brachial artery FMD and nitroglycerin-mediated dilation (NTG) using high resolution ultrasound. Patients with CAD were more often diabetic, hypertensive, obese, dyslipidemic, and smoked more than controls. Aspirin, Clopidogrel, angiotensin-converting enzymes inhibitors, beta-blockers, and statins were also significantly more common in patients with CAD than in controls. At baseline, FMD, but not NTG, was significantly lower in patients with CAD compared to controls. Acute caffeine ingestion significantly increased FMD but not NTG and significantly decreased high-sensitivity C-reactive protein in the 2 groups compared to placebo. ‘In conclusion, acute caffeine ingestion significantly improved endothelial function assessed by brachial artery FMD in subjects with and without CAD and was associated with lower plasma markers of inflammation’.