Introduction: Echocardiographic assessment of RV function is problematic. Systolic velocity of the tricuspid annulus (tS m ) has been shown to correlate with RV ejection fraction. Furthermore, tS m is generally depressed in chronic pulmonary hypertension. We sought to evaluate RV systolic function in chronic thromboembolic pulmonary hypertension (CTEPH) using 2D speckle tracking before and after pulmonary thromboendarterectomy (PTE). Hypothesis: We hypothesized that tS m would increase after PTE. Methods: We measured tS m from 2D echocardiography using speckle tracking in 127 consecutive CTEPH patients (52 ± 14 years, 49% female) with adequate images pre- & post- PTE. tS m was measured 9.7 ± 17.3 days before and 11.3 ± 17.0 days after PTE using Epsilon Imaging EchoInsight software. Results: Unexpectedly, tS m worsened after PTE (8.2 ± 3.5 to 5.4 ± 2.8 cm/sec [p=<0.0001]). Pulmonary vascular resistance (PVR), mean pulmonary artery pressure (mPAP), and cardiac output (CO) all improved: 723 ± 258 to 246 ± 133 dyne-sec/cm 5 (p=<0.0001), 46 ± 12 to 24 ± 7 mm Hg (p=<0.0001), and 4.4 ± 1.3 to 5.6 ± 1.2 L/min (p=<0.0001) respectively after PTE (Table 2). Preoperatively, tS m correlated inversely with PVR (p=<0.0001) and mPAP (p=0.003) and directly with CO (p=0.0002) (Table 1). Postoperatively, tS m did not significantly correlate with PVR, mPAP, or CO. Conclusions: tS m correlates significantly with PVR, mPAP, and CO in patients referred for CTEPH. Early after PTE, however, tS m decreases by 34% and demonstrates no correlation with postoperative right heart catheterization data. In conclusion, tS m cannot be used to accurately predict RV function immediately following successful PTE.