Background: Successful thromboendarterectomy for chronic thromboembolic pulmonary hypertension promptly improves right ventricular (RV) function by decreasing RV volume and increasing ejection fraction (EF). Single photon emission computed tomography (SPECT) equilibrium radionuclide angiocardiography (ERNA) has been validated as a measure of RV and left ventricular (LV) volume and EF. Methods and Results: Nine patients with chronic thromboembolic pulmonary hypertension underwent electron beam computed tomography (EBCT) and SPECT ERNA cardiac studies before and after thromboendarterectomy. EBCT and SPECT ERNA measures of RV and LV volume and EF were compared. Before thromboendarterectomy, EBCT and SPECT ERNA RV and LV volumes and RV EF were similar. LV EF was within the normal range with both methods but was slightly greater (P = .004) when measured by EBCT (mean ± SD, 0.61 ± 0.08) compared with SPECT ERNA (0.54 ± 0.10). Thromboendarterectomy measured by EBCT and SPECT ERNA produced marked similar and significant decreases in RV end-systolic (-72 ± 59 mL vs -58 ± 25 mL) and end-diastolic (-75 ± 85 mL vs -76 ± 32 mL) volumes and similar slight increases in RV EF (0.12 ± 0.07 vs 0.05 ± 0.06). Slight decreases in mean LV end-systolic (-19 ± 23 mL vs -5 ± 13 mL, P = .05) and end-diastolic (-32 ± 53 mL vs -9 ± 31 mL, P = .21) volumes occurred, with little change in mean LV EF (0.05 ± 0.07 vs 0.00 ± 0.10). Conclusions: SPECT ERNA is an accurate method for measuring RV and LV volume and EF before and after thromboendarterectomy. © 2007 American Society of Nuclear Cardiology.