Select the true statement in regards to healthy cardiac muscle. Neither summation nor tetany can occur. Neither summation nor tetany can occur. Both summation and tetany can occur. Both summation and tetany can occur. Summation, but not tetany, can occur. Summation, but not tetany, can occur. Tetany, but not summation, can occur. Tetany, but not summation, can occur. The refractory period of a normal cardiac muscle cell is relatively short. The refractory period of a normal cardiac muscle cell is relatively short.