Potassium is a mineral in the body that helps maintain fluid balance, nerve function, and muscle contraction, as well as the proper transmission of electrical impulses in the heart. Potatoes and bananas are especially good sources of potassium, which also is found in many meats, milks, fruits, vegetables, and grains.
Both low and high potassium levels can disrupt the normal electrical impulses in the heart, which leads to irregular heartbeats (arrhythmias).