The underlying mechanisms behind cardiac arrhythmias are described in this manuscript. In clinical practice, significant arrhythmias are unpredictable, and under some conditions, potentially life-threatening. How can basic science help improve our understanding of molecular entities and factors behind the arrhythmia to advance, develop, adapt or deliver available medications? Structural heart disease and remodelling (e.g., heart failure, cardiomyopathy), the presence of modulating factors (i.e., diabetes mellitus, autonomic nervous system), genetic predispositions (i.e., channelopathies) are considerable preconditions, and influence the development of an arrhythmia. Cardiac arrhythmias may indeed share common basic mechanisms, while elements and substrates perpetuating these may be different and ultimately manifest as various ECG abnormalities. This article lists cellular and subcellular iatrogenic disorders responsible for abnormal impulse generation, or conduction disturbances, including the latest development in theories and biological research, for a better understanding of cellular disorders behind arrhythmogenesis.