<prompt> Quinidine exes action on hea byCa Channel blockerKt Channel blockerNa Channel openerCl Channel opener  <response>: Refer katzung 11e p 237 Mechanism of action Like all other class I antiarrhythmic agents, quinidine primarily works by blocking the fast inward sodium current INa. ... The effect of blocking the fast inward sodium current causes the phase 0 depolarization of the cardiac action potential to decrease decreased Vmax. 