Symptoms of hyperkalemia include muscle weakness, tetraplegia, cold extremities, loss of tendon reflexes, or extreme lethargy. The specific symptoms are related to the elevation of potassium in the blood. If the elevation is mild, between 5 and 6 mEq/L, symptoms such as weakness, coldness and loss of tendon reflexes may occur. In severe hyperkalemia, the electrocardiogram may be altered with elevated T waves, slowed heart rate, low heart sounds, atrioventricular block, or even ventricular fibrillation and cardiac arrest.