The study included 51 people with heart failure. The researchers randomly assigned them to two groups. One group was given decaffeinated coffee that contained 100 milligrams (mg) of caffeine powder. The other group received decaffeinated coffee with a milk powder. Patients drank the brews at one-hour intervals during a five-hour period. Those given caffeine received a total of 500 milligrams. The study also included a treadmill "stress" test one hour after the last cup of coffee.