Young dogs with ventricular arrhythmias (VA) are uncommon. We describe a 3-month old Irish Setter presented with episodes of collapse. Twenty-four hour ECG (Holter) monitoring revealed frequent VA and ventricular tachycardia. The rate and morphology were similar to that of the German Shepherd (GS) with inherited VA. Echocardiographic examination was normal except for a thin hyperechoic structure (Purkinje fiber) traversing the LV chamber. Movement of the structure was profound with blood flow. The dog died suddenly in the morning. Necropsy confirmed the presence of an excessively long Purkinje fiber (Pf) in the left ventricle without other abnormalities. The Holter recording of this dog was compared to 7 non GS dogs less than 10-months of age with VA and normal echo except for 2 dogs with a long Purkinje fiber. The VA amongst these dogs was similar. Therefore, similar VA in non GS young dogs exists. The role of the long Pf is speculative.