New experimental methods in cellular electrophysiology allowed the identification and characterization of specific "ion channels" in the plasma membrane of cardiac cells in different regions of the heart. Function and implication of the "ion channels" have been considered in 1) the initiation of the heart-beat, 2) the chronotropic and inotropic effects of neurotransmitters (nor-epinephrine-acetylcholine), 3) the action mechanism of the steroid cardioactive drugs, 4) the cardiac repolarization, 5) the physiopathology of several arrhythmias. Moreover clinical data useful for the indirect evaluation of the ion channels function have been pointed out, stressing the ion channels models contribution for the cardiac pathology interpretation, particularly in the cardiac arrhythmias field.