Acute heart failure (AHF) is a complex syndrome with presentations ranging from hypotensive cardiogenic shock to hypertensive emergency with pulmonary edema. Most patients with AHF present with worsening of chronic HF signs and symptoms over days to weeks, and significant heterogeneity exists. It can, therefore, be challenging to characterize the overall population. The complexity of defining the AHF phenotype has been cited as a contributing cause for neutral results in most pharmacologic trials in patients with AHF. Dyspnea has been a routine inclusion criterion for AHF for over a decade, but the utility of current instruments for dyspnea assessment has been called into question. Furthermore, the threshold of clinical severity that prompts patient admission of an HF clinic visit may vary substantially across regions in global trials. Therefore, the inclusion of cardiac-specific biomarkers has been incorporated into AHF trials as 1 strategy to support inclusion of the target patient population and potentially enrich the population with patients at risk for clinical outcomes. In conclusion, we discuss strategies to support appropriate patient selection in AHF trials with an emphasis on using biomarker criteria that may improve the likelihood of success with future AHF clinical trials.