Its really fairly rare for Water Fasting to affect your heart because of potassium depletion, however, it can happen. If you feel you must fast, then it is vital that you monitor yourself closely. A shorter than planned fast is much better than heart failure. Perhaps you would be better off doing more frequent short fasts and eating a clean healthy Diet in between. If you do have a potassium deficiency, then the raw fruits and veggies of a cleansing diet would benefit you. You might also want to consider adding 1 tablespoon of raw apple cider vinegar to a glass of water once or twice a day, cider vinegar is full of potassium and other healthful minerals.