Arteriovenous fistulas and hemangiosarcoma can share a similar presentation in a canine patient. Arteriovenous fistulas are abnormal communications between an artery and a vein, and they are most commonly found on the extremities. Hemangiosarcoma is a highly malignant vascular neoplasm. This case report details the work-up and surgical treatment of a presumptive arteriovenous fistula on the hind limb of a young adult Weimaraner. The lesion was removed and histopathology revealed cellular characteristics consistent with hemangiosarcoma. At an eight month follow-up with the owner, the patient was doing well, with no signs of recurrence or metastatic disease.