Thermodilution is a method of measuring blood flow. A cold electrolyte solution is injected through the proximal port of the PA catheter into the right atrium. The cold fluid mixes with blood in the right heart chambers and the cooled blood is ejected into the pulmonary artery, where it flows past a thermistor located at the distal end of the PA catheter. The changes in blood temperature over time recorded by the thermistor are used to create a temperature-time curve; the area under this curve is equivalent to the average cardiac output in the absence of intracardiac shunts. In the case of tricuspid regurgitation, the cold fluid is delayed in the right heart because of back-and-forth movement across the incompetent valve, thus leading to a prolonged thermodilution curve. This produces a falsely low cardiac output.