Heart valve and strings, coloured scanning electron micrograph (SEM). This is the mitral valve (upper left), controlling the blood flow between two of the hearts chambers, the left atrium and the left ventricle (seen here). The heart strings (threadlike structures) are known as the chordae tendineae, and are controlled by the papilliary muscles. The structures at centre, known as trabeculae carneae, are muscular, columnar protrusions found on the internal surface of the ventricles.
