Aortic regurgitation (AR) can be a normal function of aging or a disease in younger horses. Symptoms range from no outward signs to decreased performance to sudden cardiac arrest. My study used 3-D echocardiography, ultrasound of the heart, to look at the equine aortic valve and assess it for AR severity. Three-dimensional echocardiography records a pyramid of tissue rather than a 2-D plane, showing cardiac structures difficult to visualize in standard 2-D methods. In normal valves, only the edges of the cusps were visible, as the tissue is very thin when images were taken from the right, which is standard positioning for imaging the aortic valve. I observed the cusps of the aortic valve to be thickened in horses with AR, with degree of thickening corresponding to AR severity. Left-sided images were generally worse quality than right-sided, but in some cases there was better visualization of some aspects of the aortic valve in left-sided images. 3-D echocardiography potentially could be used as a standard for diagnosis of AR, specifically by looking at cusp thicknesses, and could more specifically diagnose which part of the valve is affected by disease.