MacCallum patch/plaque is a feature of chronic rheumatic hea disease (RHD). During mitral regurgitation, where the regurgitant jet strikes back the atrial wall, results in endocardial thickening and it is called MacCallum patch or MacCallum plaques. They are described as "map-like areas of thickened, roughened, and wrinkled pa of the endocardium in the left atrium", usually associated with dilated left atrium.