ObjectiveTo assess the effects of heart rate, right ventricular systolic performance (ejection fraction), chamber dimensions, and flow rate (cardiac index) on the reproducibility of algorithm-derived triplicate thermodilution right ventricular ejection fraction measurements.DesignProspective study; combined hemodynamic and echocardiographic clinical evaluation.SettingOperating room in a university hospital.PatientsTwenty-one coronary artery bypass graft patients.Measurements and Main ResultsThe right atrial delivery site was positioned by analysis of transduced pressure waveform and echocardiographic imaging of tracer agitated saline cavitations. Measurement reproducibility was quantified by determining the variation (standard deviation) within 101 triplicate thermodilution measurement sets. There was no significant relationship between measurement reproducibility and estimates of right atrial area (21.6 ± 6.9 cm2), diameter (5.1 ± 0.8 cm) and supero-inferior length (5.1 ± 0.9 cm) and right ventricular maximal minor axis diastolic diameter (4.21 ± 1.05 cm). Reproducibility was also unrelated to right ventricular end-diastolic volume index (97.9 ± 32.7 mL/m2) and cardiac index (2.9 ± 0.9 L/min/m2). Measurement reproducibility was directly related to mean right ventricular ejection fraction (0.39 ± 0.14) and inversely related to heart rate (80.8 ± 18.6 beats/min) (p< .01 and < .001, respectively).ConclusionsThermodilution-derived right ventricular ejection fraction measurement reproducibility was unrelated to estimates of right atrial and ventricular dimensions and cardiac index. Measurement reproducibility was a direct function of right ventricular systolic performance and an indirect function of heart rate. Measurement should be interpreted with these constraints in mind.