For most adults, a daily caffeine habit may be safer for the heart than many people assume. A new American Heart Association review found that up to 400 milligrams of caffeine a day, roughly three to five cups of regular black coffee, is generally safe and may even be linked to lower risks of heart disease, stroke, heart failure, and Type 2 diabetes. But the source matters: highly concentrated energy drinks and shots can sharply raise blood pressure and trigger irregular heart rhythms.