Along with a worldwide epidemiological transition and dramatic increase in the elderly population, both the incidence and prevalence of heart failure (HF) are increasing worldwide. This epidemic of HF is characterized by an increase of HF with preserved left ventricular ejection fraction (LVEF) (HFpEF) and a decrease of HF with reduced LVEF (HFrEF). Of note, transition between HFpEF and HFrEF has been recently highlighted, since it significantly relates with prognosis. Our recent studies indicated that temporary changes in LVEF are common and associated with prognosis in patients with HF. In this chapter, we summarize recent findings on temporal changes in LVEF and their prognostic impact in HF patients, acknowledging that further studies are needed to fully elucidate the pathophysiology of LVEF recovery and deterioration to improve clinical outcomes of HF patients, and also to develop therapies targeting novel pathways of myocardial recovery.