Purpose: “Heart Function View (HFV)” is a software that performs phase analysis as well as functional assessment of the left ventricle (LV) using myocardial perfusion single photon emission computed tomography (SPECT) (MPS). Phase analysis-derived phase standard deviation (PhSD) and histogram bandwidth (PhHB) are good indices for detecting LV dyssyncrony. We aimed to examine whether PhHB and/or PhSD (PhHB/PhSD) are useful clinical indicators that reflect the severity of heart failure (HF) in comparison with the LV ejection fraction (EF). Methods: Patients underwent 99mTc-tetrofosmin quantitative gated MPS including treadmill exercise. In HFV analyses, patients with induced ischemia were excluded. Phase and time-volume curve analyses were performed using HFV (n=66). Results: PhHB/PhSD correlated with LV end-diastolic volume (EDV), end-systolic volume (ESV), the first-third filling fraction (1/3FF), and peak filling rate (PFR) as well as echocardiography tissue Doppler-derived E/e’ as hemodynamic parameters of HF severity. LVEF also correlated with these hemodynamic parameters, except for 1/3FF. PhHB/PhSD positively correlated with log BNP as a neurohumoral marker of HF severity. LVEF negatively correlated with log BNP. PhHB/PhSD negatively correlated with exercise capacity as physiological indicators of HF severity, whereas LVEF did not. PhHB/PhSD were significantly greater in patients receiving cardiac resynchronization therapy (CRT, n=6) than in non-CRT patients (n=66), whereas LVEF were lower. Conclusion: PhHB/PhSD, similar to LVEF, are useful clinical indicators for evaluating HF severity. However, the clinical significance of LVEF and PhHB/PhSD differ. Thus, a phase analysis may additively offer useful information for the management of HF.