Bananas
One banana has 422 mg—about 12 percent of your recommended daily dose—of potassium. The potassium in bananas helps maintain normal heart function and the balance of sodium and water in the body. Potassium helps the kidneys excrete excess sodium, thereby contributing to healthy blood pressure. This mineral is especially important for people taking diuretics for heart disease, which combat sodium and water retention but also strip potassium from the body in the process. Other good sources include sweet potatoes (694 mg for one medium), nonfat yogurt (579 mg for 1 cup) and spinach (419 mg for 1/2 cup, cooked).