Cardiac veins
Cardiac Vein Drainage: Triple System
The cardiac veins are organized into three distinct systems, each playing a crucial role in draining deoxygenated blood from the heart muscles back into circulation.
The first system is centered around the coronary sinus, into which the majority of the cardiac veins discharge. This system includes the great cardiac vein, the middle cardiac vein, the small cardiac vein, and the posterior cardiac vein. Collectively, these veins drain blood from various parts of the heart and channel it into the right atrium through the coronary sinus.
The second system comprises veins that bypass the coronary sinus altogether, opting instead to drain directly into the right atrium. This arrangement ensures that the heart efficiently recycles its blood supply.
The third system consists of small veins that drain directly into the heart.
First system: centred around the coronary sinus
Coronary sinus
First, we will examine the coronary sinus, which is located on the posterior side of the heart. It runs transversely in the left coronary sulcus (atrioventricular groove) and empties into the right atrium. Its opening is located just medial to the opening of the inferior vena cava in the right atrium.
Great cardiac vein
The great cardiac vein is a major vessel that originates at the apex of the heart. It is responsible for draining the left ventricular apex, the anterior interventricular septum, and the anterior portions of both ventricles, as well as part of the left atrium. This vein travels alongside the anterior interventricular artery—initially known as the anterior interventricular vein—and runs within the left coronary sulcus (atrioventricular groove) adjacent to the left circumflex artery. As it courses along the coronary sulcus on the left side of the heart, the vein gradually enlarges and ultimately becomes continuous with the coronary sinus. This critical transition occurs as the great cardiac vein merges with the left part of the coronary sinus, forming a single pathway that empties into the right upper part of the heart.
Anterior interventricular vein
The anterior interventricular vein, as previously mentioned, starts at the front of the heart and joins up with the great cardiac vein. It runs along a groove on the front of the heart, parallel to the left anterior descending coronary artery. This vein aids in draining blood from the left ventricular apex, the anterior interventricular septum, and the anterior portions of both ventricles.
Left marginal vein of heart
Another vein related to the great cardiac vein is the left marginal vein, which drains the lateral walls of the left ventricle. It ascends toward the great cardiac vein, where it commonly empties. Its exact point of entry can vary: sometimes it opens into the first part of the coronary sinus, and at other times, it connects directly with the great cardiac vein.
Inferior vein of left ventricle
If we examine the heart more towards its inferior surface we can see a vein, that drains a part of the inferior wall of the left ventricle, this is knows as the Inferior vein of left ventricle. It usually joins the great cardiac vein or the coronary sinus and is located on the left ventricle’s back surface.
Oblique vein of left atrium
If we direct our attention towards the left atrium, we can observe a small vessel that collects blood from the left atrium. It typically merges with either the great cardiac vein or the coronary sinus. This vessel is known as the oblique vein of the left atrium or the oblique vein of Marshall. It also marks a delineation point between the great cardiac vein and the coronary sinus.
Middle cardiac vein
Examining the heart’s inferior aspect, particularly next to the inferior interventriuclar sulcus (posterior interventricular groove), we can see the middle cardiac vein ascending alongside the inferior interventricular artery and ultimately draining into the coronary sinus. This vein progresses upward within the posterior interventricular groove, closely accompanied by the inferior interventricular artery posterior interventricular artery (PDA), and empties its contents near the end of the coronary sinus.
Small cardiac vein
Upon inspecting the heart near the right atrium, it’s a group of veins is noticeable, among these there is one that runs parallel to the right coronary artery in the right atrioventricular groove, this is known as the small cardiac vein. This vein collects blood from both the right ventricle and right atrium.
Right marginal vein of heart
If we direct our attention toward the heart’s right margin, we can see a vein that runs alongside the right marginal artery. This is known as the right marginal vein, which closely ascends toward the atrium along the lateral side of the right ventricle. It typically connects with the small cardiac vein.
Second system: veins that bypass the coronary sinus
Anterior cardiac veins
When examining the anterior surface of the heart, it is evident that there is a group of veins which do not empty into the coronary sinus; instead, they directly empty into the right atrium. These are identified as the anterior cardiac veins. The anterior cardiac veins are a variable group of veins that drain a significant portion of the right ventricle.