Heart Tumors (Myocardial) in Dogs

By PetMD Editorial on Sep. 19, 2008

Myocardial Tumors

Myocardial tumors refer to tumors that specifically affect the heart. These types of tumors are rare, and when they do occur, they tend to occur in older dogs. Benign tumors are masses of tissue that do not metastasize, whereas malignant tumors metastasize throughout the body. Abnormal tissue growth arising from the blood vessels in the heart can be malignant, as with hemangiosarcomas — rare, rapidly reproducing tissue growths; or they may be benign, as is the case with hemangiomas — harmless growths consisting mainly of newly formed blood or lymph vessels.

When a tumor arises from the fibrous tissue, like heart valve tissue, the tumor is called a fibroma if it is benign, and a fibrosarcoma if it is malignant. There are also tumors that develop in the softer, connective tissue in the upper chambers of the heart (atria). Benign tumors of this sort are called myxomas, and malignant tumors are called myxosarcomas. Tumors that arise from the skeletal muscle in the heart are referred to as rhabdomyosarcomas, and they are always malignant.

There are also tumors that can spread to the heart secondarily. Some tumors which do not arise in the heart, but which spread to it are: lymphomas - malignant tumors of the lymph nodes; neurofibromas - benign tumors of nerve fiber origin; granular cell tumors - origin is unknown, and they can be malignant or benign; and osteosarcomas - malignant tumors that originate in the bone.

Symptoms and Types

Symptoms are dependent on what type of tumor is in the heart, and where it is located in the heart:

  • Heart rhythm abnormalities (cardiac arrhythmia)
  • Heart murmurs
  • Enlargement of the heart
  • Sudden heart failure
  • Signs of heart failure due to heart tumor
    • Coughing
    • Difficulty breathing, even while at rest
    • Sudden collapse
    • Exercise intolerance
    • General fatigue
    • Fainting
    • Lack of appetite
    • Bloated, fluid filled abdomen


The causes for myocardial tumors are unknown.


Your veterinarian will perform a thorough physical exam on your dog, including a baseline blood work profile. This will include a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel. A chest x-ray and ultrasound imaging will allow your veterinarian to visually examine the heart, so that a complete assessment can be made of the heart and any masses that are present within it. 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 biopsy.


Even if the mass in the heart is extensive, or has begun to spread through the body, surgical resection is still the recommended treatment of choice for most heart tumors. This holds even if the surgery will not cure the condition, but if the tumor is benign, surgical resection may be curative. Chemotherapy can be administered in the case of malignant heart tumors, but unfortunately, in many cases patients will die in spite of treatment.

Living and Management

Your veterinarian will schedule follow-up appointments for in order to perform serial heart ultrasounds on your dog. These examinations will help your doctor to follow the progress of your dog’s condition, as well as to check the heart muscle for signs of doxorubicin toxicity — if doxorubicin has been prescribed as part of a chemotherapeutic program. Doxorubicin is an effective drug for treating malignant cancers, but one of the negative side effects is that it can damage heart muscle. Your veterinarian will also take chest x-rays at each visit to make sure the tumor has not spread into any other parts of your dog's body. The final prognosis for most malignant myocardial tumors is guarded to poor.

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