Cardiac output (CO) is a key determinant of oxygen delivery, but choosing the optimal method to obtain CO in pediatric patients remains challenging. The pressure recording analytical method (PRAM), implemented in the MostCareUp system (Vygon), is an invasive uncalibrated pulse wave analysis (PWA) method to measure CO. The objective of this study is to compare CO measured by PRAM (PRAM-CO; test method) with CO simultaneously measured by transesophageal Doppler echocardiography (TEE-CO; reference method) in pediatric patients. In this prospective observational method comparison study, PRAM-CO and TEE-CO were assessed in pediatric elective cardiac surgery patients at 2 time points: after anesthesia induction and after surgery. The study was performed in a German university medical center from March 2019 to March 2020. We included pediatric patients scheduled for elective cardiac surgery with arterial catheter and TEE monitoring. PRAM-CO and TEE-CO were compared using Bland-Altman analysis accounting for repeated measurements per subject, and the percentage error (PE). We included 52 PRAM-CO and TEE-CO measurement pairs of 30 patients in the final analysis. Mean ± SD TEE-CO was 2.15 ± 1.31 L/min (range 0.55-6.07 L/min), and mean PRAM-CO was 2.21 ± 1.38 L/min (range 0.55-5.90 L/min). The mean of the differences between TEE-CO and PRAM-CO was -0.06 ±0.38 L/min with 95% limits of agreement (LOA) of 0.69 (95% confidence interval [CI], 0.53-0.82 L/min) to -0.80 L/min (95% CI, -1.00 to -0.57 L/min). The resulting PE was 34% (95% CI, 27%-41%). With a PE of <45%, PRAM-CO shows clinically acceptable agreement with TEE-CO in hemodynamically stable pediatric patients before and after cardiac surgery.