The symptoms of hemangiosarcoma in dogs depend on the location of the tumor.
Splenic Hemangiosarcom in Dogs (spleen)
In the early stages, splenic hemangiosarcoma displays very few signs. It is usually detected when the tumor has already ruptured.
Symptoms: abdominal distention, anemia, weakness, internal bleeding, pale gums, loss of appetite
Cardiac Hemangiosarcoma in Dogs (heart)
The tumor often develops on the right atrium. When it ruptures, it may cause to pericardial effusion and cardiac tamponade. This is where blood fills up around the heart and exerts pressure on it.
Symptoms: abnormal fluid (blood) buildup around the heart, abdominal distention, difficulty in breathing, abnormal heartbeat, right heart failure, collapse, weakness.
Cutaneous and Subcutaneous Hemangiosarcoma in Dogs (skin)
Tumors can form on (cutaneous) or under (subcutaneous) the skin, and some are due to sun exposure. They tend to develop on the abdomen or parts of the body with sparse or white fur.
Symptoms: Dark or red mass or lump
Hemangiosarcoma of the skin of a seven year old Bullmastiff. The tumor is about one centimeter in width.
Photo by Joel Mills (Own work) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0/), via Wikimedia Commons