Heart valves:

• develop like an endocardial duplication, their surface is covered with vascular endothelium;
• the base of the valves is formed by dense connective tissue containing collagen and elastic fibers and having no blood vessels;
• the bases of the valves are attached to fibrous rings.

On a section cutted through the base of the rabbit's heart presented structural components of the ventricular-vascular (aortic) and atrioventricular (mitral) valves.

Aortic valve separates the lumen of aorta from the cavity of the left atrium (two of the three flaps got into the section):

• facing the aorta the outer layer of the leaflet #1, #2 contains a subendothelial layer with a dense network of elastic and collagen fibers; on the atrial side it is thin, formed by a looser connective tissue #1, #2;
• the base of the flap is attached to the fibrous ring, in the center containing a section of fibrocartilage;
• in the area of the free edges, the flap contains a rounded connective tissue thickening (Arancius nodule), tendon chords are absent.

A bicuspid (mitral) valve separates the lumen of the left atrium from the left ventricle:

• the central part of the flap is flat, formed by dense connective tissue;
• the bases of the flaps are attached to the fibrous ring #1, #2 and contain sections of the myocardium #1, #2;
• on the atrial side of the valve, the subendothelial layer is thickened and contains a dense network of elastic fibers;
• the ventricular side of the valve is uneven, the connective tissue base is looser, with a small amount of elastic fibers;
• from the free edge of the flap departs the tendon chord.