Aortic stenosis
Aortic stenosis is a congenital disease in dogs characterized by left ventricular outflow tract obstruction. It is inherited in Newfoundlands, and also found in Golden Retrievers, Rottweilers, Boxers, Bulldogs, German Shepherd Dogs, and Samoyeds. Signs include fainting and exercise intolerance.

Atrial septal defect
Atrial septal defect is a hole in the division between the heart atria. It is an uncommon condition in dogs. Most are not clinically significant, but large defects may cause heart failure, cyanosis, and exercise intolerance.

Congestive heart failure
Congestive heart failure is any heart disease that results in the inability to put out enough blood to meet the dog's needs. It can be caused by the above two diseases, heat stroke, electric shock, injury, infection, developmental heart defects, or high blood pressure. Signs depend on which side of the heart is affected. Left-sided heart failure may result in coughing and difficulty breathing from a build-up of fluid in the lungs (pulmonary edema) and fainting. Right-sided heart failure may result in a build-up of fluid in the abdomen (ascites), fluid around the lungs (pleural effusion), or peripheral edema.

Cor triatriatum
Cor triatriatum, specifically cor triatriatum dexter, occurs in dogs and is characterized by a fibrous division of the right atrium. It can be treated by balloon valvuloplasty.

Degenerative mitral valve disease
Degenerative mitral valve disease is a common cause of congestive heart failure in dogs, especially small, older dogs. The leaflets of the valve become thickened and nodular, leading to mitral valve regurgitation and volume overload of the left side of the heart. Cavalier King Charles Spaniels have an inherited form of this disease.

Dilated cardiomyopathy
Dilated cardiomyopathy is a disease of heart muscle resulting in atrial and ventricular dilation. It is seen in large dog breeds such as Boxers, Great Danes, and Dobermanns. It is usually idiopathic, but can also be caused by taurine deficiency in Cocker Spaniels or doxorubicin use. Dilated cardiomyopathy usually results in congestive heart failure.

Heart valve dysplasia
Heart valve dysplasia (including mitral and tricuspid valve dysplasia) is a congenital heart defect in dogs. Dysplasia of the mitral and tricuspid valves - also known as the atrioventricular (AV) valves - can appear as thickened, shortened, or notched valves.

Hemolytic anemia
Hemolytic anemia is a type of regenerative anemia found in dogs characterized by destruction of the red blood cell. The most important type is immune-mediated hemolytic anemia, which can be a primary disease or secondary to cancer, infection, drugs, or vaccinations. Antibodies are present on the cell surface, leading to lysis and severe anemia. Other causes of hemolytic lesion include hypophosphatemia, exposure to toxins such as lead, infections such as ehrlichiosis or babesiosis, and rarely, neonatal isoerythrolysis. The behavioral condition pica, especially when involving the eating of concrete dust, tile grout, or sand, may be a sign of hemolytic anemia, indicating the need for a complete blood count to investigate a possible diagnosis.

Patent ductus arteriosus
Patent ductus arteriosus is the most common congenital heart defect in dogs in the United States. It is inherited in toy and miniature Poodles, and seen commonly in Pomeranians, Bichon Frises, and Malteses. Signs include cough and exercise intolerance.

Pericardial effusion
Pericardial effusion is a collection of fluid in the pericardium. It is usually serous (clear or yellow fluid) or serosanguinous (bloody fluid). Serious accumulation is caused by heart failure, peritoneopericardial diaphragmatic hernias, uremia, pericardial cysts, or hypoalbuminemia. Serosanguinous accumulation can be caused by cancer, usually hemangiosarcoma, idiopathic disease, trauma, clotting disorders, or left atrial rupture. Rarely pericardial effusion can be caused by infection and consist of pus. Drainage of the fluid is the ideal treatment.