Author's summary Ischemic burden was calculated with the use of semi-quantitative single photon emission computed tomography (SPECT) analysis in 165 patients with single vessel chronic total occlusion (CTO) >2.5 mm in an epicardial coronary artery. High-ischemic burden (ischemic burden >10%) was observed in 66 patients (40.0%), and in 47 patients (50.5%) of the left anterior descending (LAD) CTO. Ischemic burden was different according to the CTO location only in LAD CTO. The statistically significant predictors for high-ischemic burden were hypertension, baseline ejection fraction >45%, LAD CTO, proximal CTO location, and de novo CTO. Japanese-CTO score and Rentrop scale collateral grade were not associated with high-ischemic burden.