Cardiac arrhythmias present a number of challenges for the clinician. In all cases, any identified predisposing conditions should be managed, as possible. Signalment can be particularly important because some breeds have an increased prevalence of diseases associated with sudden arrhythmic death, including Boxers and Doberman Pinschers. The abolition of arrhythmias during exercise often is a favorable sign; whereas, their provocation with exertion is concerning, and in a horse, potentially dangerous to people. Cardiac arrhythmias can vary tremendously in frequency and severity over time. Ectopic complexes are identified and classified, as possible, by origin, site, and timing. Standards for choosing and continuing antiarrhythmic therapy are not clearly defined for many situations. Antiarrhythmic drugs might suppress potentially life-saving ventricular escape rhythms. Treatment goals for the individual patient also should be defined. Potential adverse effects of an antiarrhythmic drug must be considered against the desired benefits.