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Heart Tumors (Myocardial) in Dogs

Myocardial Tumors

Myocardial tumors are a rare occurrence, primarily affecting older dogs. These tumors can be classified as either benign or malignant. Benign tumors, which do not spread, include hemangiomas, arising from blood vessels, and fibromas, developing from fibrous tissue like heart valves. Malignant tumors, capable of metastasizing, encompass hemangiosarcomas, originating from blood vessels, and fibrosarcomas, arising from fibrous tissue.

Within the softer connective tissue of the heart’s upper chambers, benign myxomas and malignant myxosarcomas can form. Rhabdomyosarcomas, arising from skeletal muscle in the heart, are always malignant. Additionally, secondary tumors can spread to the heart from elsewhere in the body. These include lymphomas, neurofibromas, granular cell tumors, and osteosarcomas, each with distinct origins and potential for malignancy.

Symptoms and Types

The symptoms of myocardial tumors vary depending on the type and location within the heart:

  • Cardiac arrhythmias (abnormal heart rhythms)
  • Heart murmurs
  • Enlargement of the heart
  • Sudden onset of heart failure
  • Signs of heart failure attributed to a heart tumor
  • Persistent coughing
  • Difficulty breathing, even when resting
  • Sudden collapse
  • Inability to tolerate exercise
  • Overall fatigue
  • Fainting spells
  • Loss of appetite
  • Swollen, fluid-filled abdomen


The exact causes of myocardial tumors remain unknown.


Your veterinarian will conduct a comprehensive physical examination of your dog, along with baseline blood work, including a chemical blood profile, complete blood count, urinalysis, and electrolyte panel. Chest x-rays and ultrasound imaging will be utilized to visually assess the heart and any present masses. An electrocardiogram (ECG or EKG) will examine the heart’s electrical currents for abnormalities in cardiac conduction. Additionally, your veterinarian may perform a biopsy by surgically extracting tissue samples from the mass for further examination.


Surgical resection remains the primary treatment option for most heart tumors, even in cases where the mass is extensive or has metastasized. While surgery may not always cure the condition, it is still recommended, especially if the tumor is benign as it can be curative. Chemotherapy is an option for malignant heart tumors; however, it’s important to note that despite treatment, many patients may still succumb to the disease.

Living and Management

Your veterinarian will arrange follow-up appointments to conduct serial heart ultrasounds on your dog. These examinations will allow your veterinarian to monitor the progression of your dog’s condition and assess the heart muscle for signs of doxorubicin toxicity if this medication has been prescribed as part of a chemotherapy regimen. While doxorubicin is effective in treating malignant cancers, it can also potentially damage the heart muscle. Chest x-rays will also be taken at each visit to ensure the tumor hasn’t spread to other parts of your dog’s body. The prognosis for most malignant myocardial tumors is generally guarded to poor.

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