The evolution of a large amount of heat, unexplainable by ordinary chemical reactions, was observed in an electrolytic cell with a nickel cathode and a platinum anode in a potassium carbonate-light water solution. The nickel cathode had a specially designed porous structure, based on fundamental knowledge concerning the active hydrogen electrode in alkaline solutions. An increase in the concentration of calcium ions was observed in the electrolyte, which seems to be the result of potassium-hydrogen cold fusion.