What are the symptoms of hyperkalemia (high potassium)? Many people with mild hyperkalemia have no signs or ones that are easy to dismiss. Symptoms often come and go and may come on gradually over weeks or months. Dangerously high potassium levels affect the heart and cause a sudden onset of life-threatening problems. Hyperkalemia symptoms include: Abdominal (belly) pain and diarrhea. Chest pain. Heart palpitations or arrhythmia (irregular, fast or fluttering heartbeat). Muscle weakness or numbness in limbs. Nausea and vomiting