The GUIDE-IT (Guiding Evidence Based Therapy Using Biomarker Intensified Treatment in Heart Failure) trial was designed to prospectively study the relationship between change in natriuretic peptide concentration, cardiac remodeling, and clinical events in patients with heart failure with reduced ejection fraction (HFrEF). The trial was stopped early because biomarker-guided treatment was not more effective than usual care in improving outcomes. The GUIDE-IT Echo Substudy was a prespecified substudy designed to understand the influence of biomarker-guided therapy on cardiac structure and function.