Congestion is the main reason for hospitalization in patients with acute decompensated heart failure and is an important target for therapy. However, achieving complete decongestion can be challenging. Furthermore, residual congestion before discharge from hospital is associated with a high risk of early rehospitalization and death. An improved understanding of the pathophysiology of congestion is of great importance in finding better and more personalized therapies. In this Review, we describe the two different forms of congestion – intravascular congestion and tissue congestion – and hypothesize that differentiating between and specifically treating these two different forms of congestion could improve the outcomes of patients with acute decompensated heart failure. Although the majority of these patients have a combination of both intravascular and tissue congestion, one phenotype can dominate. Each of these two forms of congestion has a different pathophysiology and requires a different diagnostic approach. We provide an overview of novel and established biomarkers, imaging modalities and mechanical techniques for identifying each type of congestion. Treatment with loop diuretics, the current cornerstone of decongestive treatment, reduces circulating blood volume and thereby reduces intravascular congestion. However, the osmolality of the circulating blood decreases with the use of loop diuretics, which might result in less immediate translocation of fluid from the tissues (lungs, abdomen and periphery) to the circulation when the plasma refill rate is exceeded. By contrast, aquaretic drugs (such as vasopressin antagonists) predominantly cause water excretion, which increases the osmolality of the circulating blood, potentially improving translocation of fluid from the tissues to the circulation and thereby relieving tissue congestion.