Heart Cancer (Hemagiosarcoma) in Cats


PetMD Editorial

Updated Aug. 24, 2022

Hemangisaroma of the Heart in Cats

A hemangiosarcoma of the heart is a tumor that originates in the blood vessels that line the heart. Hemangio refers to the blood vessels and sarcoma a type of aggressive, malignant cancer that arises from the connective tissues of the body. A hemangiosarcoma may originate in the heart, or it may have metastasized to the heart from another location in the body.

This tumor often will go undetected until complications arise. Because a hemangiosarcoma arises from the blood vessels, when it reaches an unsustainable size it will burst, often resulting in life threatening internal bleeding. Other typical symptoms relate to the size of the tumor interfering with the heart's ability to function. The pumping of blood into or out of the heart organ may be blocked or slowed, resulting in an irregular heart rhythm; the pericardial sac that surrounds the heart may become filled with blood due to burst vessels, or with fluid that places restrictive pressure on the heart; or there may be a responsive abdominal swelling that puts pressure on the heart and other organs. In addition, the blood loss may lead to a regenerative anemia, with concurrent symptoms that can confound the initial diagnosis.

Symptoms and Types

Most symptoms are seen related to complications affecting heart rather than tumor itself.

  • Difficult breathing
  • Accumulation of fluid within abdominal cavity - visible abdominal distention
  • Accumulation of fluid within thoracic (chest) cavity
  • Sudden loss of consciousness/fainting (syncope)
  • Inability to perform routine exercises
  • Trouble with coordination (ataxia)
  • Irregular heart beats/arrhythmia
  • Enlargement of the liver
  • Lethargy
  • Malaise/depression
  • Loss of appetite (anorexia)
  • Weight loss


The exact cause is still unknown.


You will need to give your veterinarian a thorough history of your cat's health, onset of symptoms, and any incidents of ill health, behavioral changes, or accidents that have recently taken place. The history you provide may give your veterinarian clues as to which organs are being primarily affected and which organs are being affected secondarily. Your cat's age, breed, and the outward symptoms that are presenting will be the initial signals for a rough diagnosis.

Routine laboratory tests include a complete blood count, biochemistry profile, and urinalysis. The blood tests may reveal anemia, as often the blood loss will lead to a state of regenerative anemia, where the body is lacking in sufficient red blood cells, but is still capable of producing more of them – though it may not be able to keep with the demand.

Your veterinarian will want to take fluid samples from both the abdomen and the chest, by abdominocentesis and pericardiocentesis respectively, for cytological analysis. This can also be used to remove excess fluid so that your cat is more comfortable. Blood found in the fluid sample is a frequent sign of hemangiosarcoma, and failure of clotting in the blood when it is drawn is another telling indication, since the body is working hard to maintain its blood balance and is using the blood clotting factors too rapidly.

An electrocardiogram (ECG, or EKG) recording can be used to examine the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat). Your veterinarian may also need to take a surgical tissue sample of the mass for examination (biopsy).

Visual diagnostic methods, such as x-rays and ultrasound of the thoracic (chest) and abdominal cavities may reveal variations in cardiac size and structure. Echocardiography is the most valuable tool for making accurate diagnosis. It will confirm the presence of fluid, structural abnormalities in the heart, the presence of a tumor mass or clot, and other aspects of tumors within the heart.




This tumor is very difficult to treat as it tends to rapidly metastasize to different locations in the body. Treatment involves treating both the primary disease as well as the complications that have arisen due to the tumor. Chemotherapy is often recommended for slowing the progression of metastasis, but this alone will not stop the disease spread. Because of the vulnerable nature of the location of this sarcoma, it is often neither practical or even possible to recommend surgery with any hopes of success. Your veterinarian may drain the fluid that has accumulated within the thoracic and/or abdominal cavity, and pain medications will be prescribed by your veterinarian to relieve your cat's discomfort.

Unfortunately, this disease has a poor prognosis, and even successful treatments may only add months to your cat's life.

Living and Management

The location of this tumor (heart) makes it especially life-threatening, so the prognosis is very poor in most patients. In almost all cases, tumor metastasis has already taken place into the lungs at the time of diagnosis, making treatment more difficult. Even after surgery, recurrence is common. The life expectancy for affected animals is less than six months.

Watch for symptoms associated with recurrence and involvement of other body sites. If you notice your cat having difficulty breathing, sudden behavioral changes, which may indicate metastasis to the brain, or any other symptoms, call your veterinarian. Your veterinarian will prescribe a pain protocol for your cat, as well as a diet that is especially designed for cancer patients.

Consult your veterinarian for advice on making your cat as comfortable as possible, as end of life arrangements may need to made as the hemangiosarcoma progresses.

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