After the bidirectional cavopulmonary or Fontan operation, the physiologic consequence is passive flow of the systemic venous return to the pulmonary arteries. Knowledge of pulmonary artery pressure (PA) is valuable in the management of these patients, and obtaining this information without the need for a central line or cardiac catheterization would be advantageous. The aim of this study was to evaluate the correlation between upper extremity peripheral venous (PV) pressures and PA or superior vena cava (SVC) pressures in patients who have undergone cavopulmonary or Fontan connections. During cardiac catheterization, 19 patients with complex cyanotic heart disease who had undergone a cavopulmonary shunt or Fontan procedure were studied. Simultaneous pressure measurements were obtained from the peripheral intravenous line placed prior to the procedure and the SVC or PA. The mean pressures were compared. The mean PV pressure was 17.5 ± 5.6 mmHg. The mean SVC or PA pressure was 16.1 ± 5.4 mmHg. The mean difference was 1.5 ± 1.5 mmHg (p < 0.001). The correlation coefficient PV to SVC or PA pressure was 0.97 (p < 0.001). PV pressure measurements taken from an upper extremity accurately reflect PA pressures in patients who have undergone a cavopulmonary shunt or Fontan procedure.