Abstract: We report a case of a dog, male, eleven year old, american cocker spaniel with a history of acute dyspnea and exercise intolerance. The electrocardiography examination revealed the presence of ventricular arrhytmias, and, through echocardiographic examination, the patient was diagnosed with dilated cardiomyopathy and congestive heart failure. Treatment was performed, with improvement in congestive signs and arrhytmias. Ventricular arrhytmias are difficult to control in patients treated only for underlying heart disease, without the administration of antiarrythmics. The patient survived for fifteen months, emphasizing the need for early diagnosis and treatment, in order to obtain an improvement in life expectancy of patients with heart disease.