Coronary sinus narrowing device (reducer) implantation has emerged as an effective treatment to improve the quality of life and functional capacity in patients suffering from disabling refractory angina. Left ventricle global longitudinal strain (LV-GLS) is a useful tool for early diagnosis of subclinical cardiac injury and an independent predictor for coronary artery disease. We aimed to investigate whether LV-GLS could help predict clinical improvement after coronary sinus reducer implantation. LV-GLS assessments were performed at baseline and 6 months after reducer implantation in consecutive patients treated for refractory angina. Patients were divided into 2 groups based on reduced (<17% absolute value) or preserved baseline LV-GLS. Clinical improvement was defined as an increase of ≥25 m in the 6-minute walk test (6MWT) at follow-up. Overall, 41 patients were included, 31 in the reduced LV-GLS group and 10 in the preserved LV-GLS group. The mean age was 68 ± 8 years, with only 2 female patients (5%). Baseline characteristics did not differ significantly between the 2 groups. Univariable analysis revealed that LV-GLS was the only significant predictor for 6MWT improvement. Baseline preserved LV-GLS reduced the likelihood of 6MWT improvement by 82% (odds ratio 0.18 [0.04 to 0.83], p = 0.029). A significant increase in 6MWT (307 ± 97 m to 343 ± 92 m, p = 0.017) was observed in the reduced LV-GLS group, compared with a decrease in the preserved LV-GLS group (378 ± 86 m to 361 ± 123 m, p = 0.651). In conclusion, reduced LV-GLS may serve as a marker for potential clinical improvement in patients with refractory angina treated with reducer. Larger clinical trials are needed to establish its role.