Which of the following is NOT a physiologic characteristic of cardiac muscle?

Tetanus cannot be produced in cardiac muscle because it has a long refractory period during which it is refractory to any stimulus occurring during contraction phase. The refractory period in ventricles is 250-300 msec and about 150 msec in atria. It is of two types: absolute refractory period and relative refractory period. In absolute refractory period the cardiac muscle does not show any response at all. During relative refractory period the muscle shows response if strength of the stimulus is increased to maximum. Ref: Essentials of Medical Physiology By Khurana page 138