BACKGROUND: Stress phase bandwidth (SPBW), assessed using single-photon emission computed tomography (SPECT), is considered to be a useful indicator of left ventricular dyssynchrony. However, few reports have examined whether it can be used as an indicator for improvement of left ventricular ejection fraction (LVEF) in new-onset heart failure with reduced ejection fraction (HFrEF). METHODS AND RESULTS: A total of 64 patients (mean age 56 years, 39 male) who were admitted to our hospital with new-onset non-ischemic HFrEF (median LVEF 24.7%) from January 2018 to December 2022 in the SAKURA-HF registry and underwent SPECT were enrolled. The relationship between SPBW in the acute phase and LVEF improvement in the chronic phase was retrospectively investigated in the present study. LVEF improved significantly in the 36 patients (from 27.1 to 62.8%, p <
0.001). Guideline-directed medical therapy in both groups was comparable. SPBW was significantly lower in the group with improved LVEF (median 55.5° vs. 79.0°, p = 0.010). Logistic regression analysis revealed that SPBW was an independent predictor for LVEF improvement. Moreover, an SPBW of 71.0° was suggested as a possible cut-off value. CONCLUSIONS: SPBW may predict the improvement of LVEF in new-onset non-ischemic HFrEF, suggesting its potential utility in heart failure management.