A veterinarian often diagnoses cardiovascular disease by reviewing the medical history and signs, conducting a physical examination, and interpreting the results of specific tests or imaging procedures. The physical examination includes using a stethoscope to listen to the sounds made by the horse’s internal organs, especially the heart, lungs, and abdominal organs. A veterinarian may hear an abnormal heart rate (for example, a rate that is too slow, fast, or irregular), an abnormal breathing rate (fast or labored breathing), a murmur (an abnormal sound caused by abnormal blood flow or vibrations in the heart), decreased or muffled heart sounds, or abnormal sounds in the lungs that suggest fluid accumulation. A veterinarian will also feel the horse's pulse (which may feel rapid, weak, or irregular) and examine the horse's gums for evidence of blue, purple, or grey color, a sign that oxygen is not reaching the body's tissues adequately. The veterinarian will also examine the limbs and abdomen for signs of fluid accumulation.
Imaging techniques include x‑rays (which are not commonly performed in horses due to their size), electrocardiography (recording electrical activity of the heart), and echocardiography (a type of ultrasonography).
Most cardiovascular diseases can be diagnosed by physical examination and x‑rays. Electrocardiography is a specific test for diagnosis of arrhythmias. Echocardiography is excellent for confirming tentative diagnoses, assessing the appearance and function of heart valves, evaluating the size of the heart chamber and vessels, assessing heart muscle function, diagnosing high blood pressure in the lungs, identifying birth defects in the heart, detecting heart tumors, or detecting pericardial disease. Occasionally, more specialized tests such as cardiac catheterization (-using a thin flexible tube inserted and threaded through an artery into the heart) or nuclear studies (x-ray tests that include injection of radioactive isotopes) are necessary.
Horses with heart disorders or defects may have a general loss of condition, become fatigued easily (particularly after exercise), have difficulty breathing or shortness of breath, and show signs of weakness (including fainting or collapse). In addition, excess fluid that has accumulated in the lungs, limbs, jugular vein, under the chest or abdomen may indicate heart failure. Horses can cough because of this fluid accumulation. Signs may show up only after exercise, but over time they may occur even when the horse is at rest.
Also see professional veterinary content regarding diagnosis of cardiovascular disease.