When a person presents with cardiac arrhythmias into the emergency room, it is always worthwhile having a quick evaluation for potential causes of cardiac arrhythmias. By and large the large majority of arrhythmias in an adult is secondary to ischemic heart disease while in children inherited arrhythmogenic disorders may have to be thought of more frequently. Electrolyte imbalances and hypoxia are important in all age groups. Sometimes the underlying mechanism of electrolyte imbalnce may be subtle like refractory hypokalemia when it is associated with hypomagnesemia. It is difficult to correct hypokalemia in the presence of hypomagnesemia without simultaneous correction of the latter as magnesium is the co-factor needed for the enzyme involved in potassium re-absorption by the kidneys. Cardiac channelopathies or disorders of the cardiac ion channels are a fascinating cause of potentially life threatening arrhythmias, though not very common. Heart muscle disorders like hypertrophic and dilated cardiomyopathies are important causes of arrhythmias and sudden cardiac death.