Among the cardiovascular system neoplasms, the most common ones affecting the heart include hemangiosarcoma and heart base tumors, specifically aortic body tumors. The chemodectoma may emerge from the aortic body on the cardiac base or from the carotid body in the neck. It is scientists' belief that the chronic hypoxia may be related to the pathogeny of this tumor. A high prevalence of chemodectoma in brachycephalic dogs is due to an anatomic conformation of the respiratory system. It is an unusual pathology amongst dogs, and 80% of these tumors are from the carotid body of elderly animals. The heart base tumor can cause pericardiac effusion, which probably responds for the most common clinical manifestation regarding this illness. Different heart neoplasms from other causes of pericardiac effusion, congestive heart failure or cardiac arrhythmia are important as well. Aortic body tumor are rarely metastatic, however, when this happens, it is frequently observed lungs and liver metastasis. Approximately 52% of animals which have aortic body tumor also have another type of neoplasm. The most commonly associated forms refer to interstitial cell tumors and thyroid carcinoma. The objective of this work is to report a clinical case of chemodectoma of a boxer dog breed, 9 years old, male, which arrived at Santa Terezinha Veterinary Hospital, presenting a clinical picture of diffuse pain, anorexia, pelvic limbs weakness, not comfortable at sternal decubitus, remaining on standing posture. At the abdominal ultrasound a discrete increase in adrenal volume and liver volume--suggesting steatosis--was noticed. One week later, the picture became worse, the animal presented cyanosis, dyspnea, and pelvic limbs weakness. A hemogram was performed and showed a leukocytes, segmented and immature neutrophil increase. Regarding the serum biochemistry, an increase on alkaline phosphatases, cholesterol and alanine aminotransferase was observed. The animal died on the referred day. At necropsy, were detected a decrease on thyroid gland volume, a great neoplastic mass adhered to the base of the heart, interpreted as chemodectoma due to its histological aspect, pulmonary metastasis on the left lobe and secondary alterations such as hemorrhage and edema of this organ. This rare and hardly diagnosed neoplasm shows a reserved prognosis, and is mostly associated with another types of neoplasm. The heart tumor can be primary or metastatic, leading to clinical alterations, most commonly among elderly, male and brachycephalic breeds.