part of part of membrane depolarization cardiac muscle cell action potential membrane depolarization during action potential membrane depolarization during cardiac muscle cell action potential The process in which cardiac muscle cell membrane potential changes in the depolarizing direction from the negative resting potential towards the positive membrane potential that will be the peak of the action potential. 2011-11-10T08:20:33Z GO:0086012 biological_process Schizosaccharomyces