Myocardiam is the muscular layer of the heart. Myocardial refers to related to myocardium. Myocardial tumors are a group of tumors that specifically affect the heart. These rare tumors mostly occur in older dogs. There are different benign and malignant forms of tumors that can affect a dog's heart. Hemangiosarcoma, for example, is a malignant tumor that arises in the blood vessels and spreads rapidly to other parts of the body. Its benign version, hemangioma, is characterized by harmless growths consisting mainly of newly formed blood or lymph vessels.
A malignant tumor of the fibrous tissues (e.g heart valve tissues) is called fibrosarcoma whereas if it is benign in nature, it is known as fibroma.
Similarly, benign tumors that develop in softer, connective tissues in the upper chambers of the heart (atria) are called myxomas while its malignant form is known as myxosarcomas. Tumors that arise from skeletal muscles of the heart are always malignant and known as rhabdomyosarcomas.
Tumors that do not originate in the heart but metastasize from other distant locations into the heart 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 depend on the type and location of the tumor in the heart. Some common symptoms of heart tumors include
Heart rhythm abnormalities (cardiac arrhythmia)
Enlargement of the heart
Sudden heart failure
Signs of heart failure due to heart tumor
Difficulty breathing, even while at rest
Lack of appetite
Bloated, fluid filled abdomen