Atrial fibrillation (AF) and heart failure (HF) are two conditions widespread on the population, especially in elderly people. When AF and HF coexist in the same patient, as frequently happens, they trigger a vicious circle of mutual influence, who dramatically hesitates in lower quality of life and in increased mortality. The relationship between AF and HF is long and vigorously investigated: it is an ever-changing field of knowledge because alongside well known and proven results, especiallythe pathophysiological ones, there are new horizons of research since many aspects are still obscure. Hence, this limit is reflected in the complexity of the combined management of AF and HF in clinical practice. It also explains an ominous prognosis despite significant therapeutic advances. In this review we go over again the well-established knowledge about the pathophysiology binder HF and AF; we provide some epidemiological, clinical and therapeutic informations, we also highlight the new acquisitions, the new research areas and, finally, the still unresolved questions.