When a tumor in the blood vessel enlarges past a certain point, it will burst and cause internal bleeding. An affected cat may appear to be fine one moment and then suddenly collapse. This is a life-threatening situation that requires immediate emergency veterinary treatment.

Hemangiosarcoma is a malignant, aggressive cancer of the endothelial cells which form blood vessels. When hemangiosarcoma occurs in the heart, it may have originated from the vessels located in the heart’s lining or metastasized from tumors in other areas of the body. Symptoms of the condition in cats are usually so subtle that it is nearly impossible to proactively diagnose. Due to its aggressive nature, by the time the tumor is noticed it will often have already metastasized to the lungs or other areas of the body.

Most visible symptoms are caused by heart complications resulting from the location of the tumor rather than from the presence of cancer. Affected cats may display one or more of the following symptoms:

A definitive cause of hemangiosarcoma has not been determined. The condition typically occurs in cats between the ages of eight to ten years. There is some speculation that it may occur more commonly in male cats and in the domestic shorthair breed.

When a cat is brought in for examination, the vet will begin by reviewing its full health history. Owners should be prepared to discuss the onset of symptoms, any accidents or illnesses that have recently been experienced, and details regarding behavioral changes.

A standard set of lab tests will be ordered including a complete blood count (CBC), biochemistry, and urinalysis. If fluid is retained in the cat’s chest or abdomen, it may be drained with a large needle to help ease pressure on the heart and lungs. It’s likely that samples of the fluid will be sent to a laboratory for testing. If blood is present in the samples, this is an indication of hemangiosarcoma. The presence of regenerative anemia or difficulty with blood clotting are also likely indicators. A physical exam may find that the abdomen is distended and the pulse may be weak.

The electrical currents within the heart may be tested using an electrocardiogram (ECG or EKG), and visual diagnostics such as X-rays, ultrasound, and echocardiogram may be ordered to aid in a positive diagnosis. The vet will be looking for additional tumors, fluid on the heart or lungs, and other heart abnormalities. It is also likely that a biopsy of the tumor tissue will be performed to positively confirm the tumor type.

Unfortunately, prognosis is very poor for cats with heart hemangiosarcoma. Successful treatment is unlikely to add much time to the cat’s life expectancy. Unless emergency surgery is needed, most treatment recommendations will be focused on minimizing pain and improving the quality of life for the cat’s remaining life expectancy.

The first time that the presence of hemangiosarcoma is noticed is often when a rupture has already occurred. In this case, life-saving emergency surgery may be necessary to stop internal bleeding. During the surgery, an attempt may be made to remove the tumor and a biopsy is likely to be performed. 

Treatment of heart hemangiosarcoma is difficult due to the proximity of the tumor to the heart and lungs and the high likelihood of metastasis. Vets will often need to treat both the cancer itself and any complications that the tumor may be causing. It is likely that a consultation with a veterinary oncologist may be needed and chemotherapy is often recommended to slow the spread of the cancerous cells. Radiation therapy may be administered once a week for three to five weeks to control actively bleeding tumors. Pain levels will be managed through the use of prescription medications.

Hemangiosarcoma is likely to recur even if surgical treatment has been successful. If the cat begins to have difficulty breathing, this may indicate a recurrence of the condition. Sudden changes in behavior may be a sign that the cancer has metastasized to the brain. Any signs of new or recurring symptoms should immediately be reported to the treating veterinarian. 

A diet specially formulated for cats with cancer may be recommended, and pain medication will likely be needed for the remainder of the cat’s life. Unfortunately, life expectancy for cats with this condition is typically less than six months.