ERP:Effective refractory period 20- RRP:Relative refractory period -20 mV -40 ERP 60 -80 -100」 100ms A:Action potential B:Mechanical contraction Significance: The cardiac muscle is refractory to any stimulus during the contraction phase and thus tetanus cannot be produced in cardiac muscle. 2. The cardiac muscle can relax and get filled up with blood and then contract to pump out the blood. ERP: Effective refractory period RRP: Relative refractory period Significance: 1. The cardiac muscle is refractory to any stimulus during the contraction phase and thus tetanus cannot be produced in cardiac muscle. 2. The cardiac muscle can relax and get filled up with blood and then contract to pump out the blood