Summary Echocardiography is an extremely versatile tool for both the equine clinician and physiologist. There are three useful forms of echocardiography, B mode, M mode and Doppler. Together they provide complementary information on cardiac disease and haemodynamic status. B mode is used to image the cardiac chambers, valves, myocardium and pericardium. M mode allows determination of motion of cardiac structures; it is superior to B mode for timing of events and it is used to make precise measurements of the heart. Doppler echocardiography can assess intracardiac blood flow and its velocity. Echocardiography has applications in all forms of equine cardiac disease. In this article the principles of, and imaging techniques used in, B mode, M mode and Doppler echocardiography in the horse are reviewed. Normal findings and abnormalities seen in association with valvular lesions, congenital cardiac disease, myocardial and pericardial diseases are discussed. Recent developments in echocardiographic techniques for assessment of ventricular function are described.