The left superior vena cava or vein of Marshall is a congenital anomaly caused by an abnormal development of the coronary sinus during the early stages of fetal life with an incidence ranging from 0.3% to 4.3% in the general population when associated to other cardiac abnormalities, but in most cases it drains into the coronary sinus and remains asymptomatic.

Named after the English physician John Marshall (1818-1891) who first described it.

Present during embryonic life, it occludes forming a fibrous ligament called the ligament of Marshall, which joins the coronary sinus with the left innominate vein. The left superior vena cava drains blood from the limb and left the left side of the head and neck into the right atrium through the coronary sinus while 8% of cases drains into the left atrium causing hemodynamic changes such as left-right shunt.

It can support the entire venous reflux of the top fields of the body. In the case of coexistence of superior vena cava, right and left, the gauge of the two will be complementary, in relation to the flow drained.

Its presence is usually not pathological, unless they are simultaneously further cardiovascular abnormalities such as ventricular septal defect or atrioventricular (50% of cases); in which case it is related to significant morbidity and mortality. The surgical treatment of the anomaly simple is therefore not necessary.

It is known to cardiology because, in case of the presence of muscle tissue, can be due to arrhythmias and atrial fibrillation.