If your baby is receiving a diuretic such as Lasix, your cardiologist may recommend a potassium supplement because some diuretics remove potassium from the body along with the excess fluid. The potassium supplement is usually given as a liquid medication added to a small amount of juice or milk to mask the bitter taste. Foods such as bananas, orange juice, potatoes and dried fruits are also a good source of potassium for older infants.