Cardiac dysfunction is often manifested as arrhythmia, with disruption of the normal periodicity and regularity of electromechanical activity. Cardiac arrhythmias, or abnormalities of cardiac rhythm, are associated with a diverse group of conditions, including congenital, metabolic, structural, physiological, and immunological, and infectious abnormalities. Dysarrhythmia may also be classified as primary because of endogenous electrical abnormalities, or secondary, because of exogenous influences such as ischemia or adrenergic stimuli. Clinical arrhythmia syndromes begin with a single asymptomatic abnormal complex that is benign, progressing to grouped, sustained complexes associated with worsened symptoms and outcome. Proper diagnosis of arrhythmia reflecting symptomology and outcome is essential in acute cardiac care.