A persistent left superior vena cava (PLSVC) is the most common thoracic venous anomaly. It is a persistent remnant of a vessel that is present as a counterpart of normal right-sided superior vena cava (SVC) in early embryological development but normally disappears later. Although it can be easily diagnosed by the characteristic chest radiographic appearance of a pulmonary artery catheter (PAC) passed through it after being inserted into the left subclavian or jugular vein, its diagnosis is usually missed by the presence of normal (right) SVC and the passage of the catheter on the right side. Its diagnosis can be confirmed by many noninvasive and invasive tests, or it is incidentally diagnosed at thoracic surgery or autopsy. If it is not associated with other congenital cardiac anomalies, it is usually asymptomatic and hemodynamically insignificant. However, PLSVC has important clinical implications in certain situations. In this article, we describe a patient with bilateral SVC (a normal right SVC and a PLSVC) identified by a PAC in the PLSVC and the pacemaker wires in the right SVC. In addition, we review the literature on prevalence, embryological development, diagnosis, and clinical implications of PLSVC.