The heart functions as a muscular pump, circulating blood throughout the body. To maintain this essential one-way flow, the heart relies on strong internal components. Among these structures are the chordae tendineae, often described simply as the heart strings. This article will explore the nature of these cords, their specific placement within the heart, and how their mechanical action ensures proper cardiac function.
Defining the Chordae Tendineae
The chordae tendineae are strong, cord-like bands of fibrous connective tissue that appear white and tendon-like. Their primary component is collagen, which provides the tensile strength needed to resist the high pressures generated within the heart’s chambers. They also contain a small amount of elastin fibers, giving them resilience and flexibility during the constant cardiac cycle movement. These strands represent a specialized support system within the heart’s lower chambers.
The appearance of the chordae tendineae, resembling the strings of a parachute, gives rise to their nickname, “heart strings”. They are classified based on their insertion point onto the valve leaflets. Marginal (primary) chords attach to the free edge, while intermediate (secondary) and basal (tertiary) chords attach to the body and base, respectively, offering additional support.
Location and Attachment Points
These connective tissue cords are found exclusively within the ventricles, the two lower pumping chambers of the heart. The chordae tendineae link two distinct anatomical structures. At one end, they insert directly into the atrioventricular (AV) valve leaflets, anchoring the two cusps of the mitral valve (left ventricle) and the three cusps of the tricuspid valve (right ventricle).
The opposite ends of the cords are firmly attached to the papillary muscles, which are small, cone-shaped muscular projections extending inward from the ventricular walls. This arrangement creates a subvalvular apparatus linking the valve leaflets to the ventricular muscle. This connection allows the chordae tendineae to perform their mechanical function.
The Mechanism of Valve Control
The role of the chordae tendineae is tied to ventricular contraction, known as systole, when the heart expels blood. As the ventricles contract, pressure inside the chambers rises dramatically, forcing the AV valves closed. This prevents blood from flowing backward into the upper chambers (atria).
Without a restraining mechanism, the immense pressure differential would cause the closed valve leaflets to flip backward, or prolapse, into the atrial cavity. The chordae tendineae act like tethers, preventing this inversion. The papillary muscles contract slightly ahead of the ventricle, pulling the cords taut and maintaining the valve leaflets in a sealed position. The chordae’s action is not to close the valves, but to anchor them against the force of the blood, ensuring blood is directed out of the heart.
Clinical Significance of Failure
When the chordae tendineae are damaged or rupture, mechanical control over the valve leaflets is compromised. Damage can occur due to degenerative diseases, trauma, or infection like endocarditis. If cords break or become too elongated, the supported valve leaflet is no longer securely tethered.
This failure allows the leaflet to swing backward into the atrium during ventricular contraction, a condition called valve prolapse. The valve seal is broken, causing blood to flow backward, known as regurgitation or a “leaky valve.” This backward flow means the heart must pump the same volume multiple times, increasing the volume load. Over time, this chronic overwork can lead to the enlargement of heart chambers and, eventually, congestive heart failure.