They tested green tea, coffee and hot water on the volunteers, whose heart and artery functions were checked each time.
Although there's evidence that black tea - the usual variety we drink in the West - there was less research into green tea, which is more usually consumed in the East. They discovered that the green tea 'significantly' increased the diameter of the artery that feeds the heart, a positive effect that happened 30 minutes afterwards. Neither coffee nor water had the same effect.
(Source: European Journal of Cardiovascular Prevention & Rehabilitation, 2008; 15: 300-5).