Acute heart failure syndrome (AHFS) is a major public health problem. It is defined as gradual or rapid change in heart failure (HF) signs and symptoms, which often results in an unplanned hospitalization and a need for urgent therapy. Many evidence-based pharmacologic, device, and surgical treatment for HF are available or under development. Despite these new treatments and improvement in survival, hospitalizations in HF have steadily increased over the last 30 years, and the post-discharge prognosis of patients hospitalized with AHFS remains poor (Gheorghiade et al. Circulation 112:3958-3968, 2005; Fonarow et al. Rev Cardiovasc Med 4:S21-30, 2003). Most hospitalizations for AHFS are related to "congestion" rather than to low cardiac output. The definition, identification, quantification, and monitoring of congestion are therefore essential in AHFS. The purpose of this article is: (1) to characterize the different types of hemodynamic, clinical, and pulmonary congestion in AHFS; (2) to focus on the different possible ways to assess pulmonary congestion (probably the most important, and up to now the most diagnostically elusive of the three types of congestions); (3) to propose new possible ways to implement objective and user-friendly measures of pulmonary congestion in clinical and scientific decision-making in AHFS in the near future.