Under physiological conditions the electrical activity of the heart begins with the sinoatrial node cells excitation. The slow diastolic depolarization of sinoatrial node cells leads to an action potential that spreads through the atria, the atrioventricular node, the His–Purkinje system and ventricular myocardium, causing their excitement. Thus, due to the electromechanical coupling the sequential contraction of the atria and the ventricles occurs. The cardiac action potential consists of 5 consecutive phases: 1) rapid depolarization phase (phase 0) is due to the opening of the fast Na+ channels causing a rapid influx of Na+ ions into the cell; 2) the early phase of rapid repolarization (phase 1); 3) slow depolarization phase or plateau (phase 2), is sustained by a balance between inward movement of Ca2+ and outward movement of K+; 4) late phase of rapid repolarization (phase 3), due to the prevailing yield of K + ions; 5) phase 4 – the resting membrane potential. Initiation and sustenance of the action potential in the myocardium is regulated by activity of the plurality of ion channels proteins. Transmembrane proteins provide a constant current of ions through the ion channels into the sarcolemma of cardiomyocytes, generating electrical impulses. Ion channels are divided into voltage-, ligand- and mechano-gated. All ion channels are composed of a α-subunit core and additional subunits. The basic structure of the ion channel is α-subunit, which determines its normal function, and β-subunits regulate only the kinetics of the channel. Proper organization of the electrical activity of the heart is carried out through the normal functioning of the cardiac ion channels. If there are mutations in genes encoding ion channel proteins, the so-called channelopathies develope, manifesting with life-threatening arrhythmias. Variety of ion channels of the heart and their functions assume an integrated approach to the diagnosis and treatment of cardiac arrhythmias. Understanding the role of ionic currents in the formation of an action potential under physiological conditions and pathological changes may contribute to the successful selection of antiarrhythmic drugs for the effective treatment of arrhythmias and their using with the least possible chance of proarrhythmogenic action. In many cases the only antiarrhythmic therapy is insufficient for effective prevention of sudden cardiac death in consequence of the life-threatening arrhythmias. This category of patients requires implantation of a cardioverter-defibrillator. In the future the widespread application of genetic and cellular technologies may solve the problem of prevention and treatment of congenital cardiac channelopathies.