Immediate antagonism of the cardiac effects of hyperkalemia is done by

Intravenous calcium serves to protect the hea. Calcium raises the action potential threshold and reduces excitability, without changing the resting membrane potential. By restoring the difference between resting and threshold potentials, calcium reverses the depolarization blockade due to hyperkalemia. The recommended dose is 10 mL of 10% calcium gluconate (3-4 mL of calcium chloride), infused intravenously over 2-3 min with cardiac monitoring. Ref: Harrison 19e pg: 312