BACKGROUND: Despite the high number of admissions for acute decompensated heart failure (ADHF), there are no specific criteria for discharge readiness. A number of patients have implantable devices that might provide data to assist in determining readiness for discharge. METHODS AND RESULTS: The 3D-HF (Diagnostic Data for Discharge in Heart Failure Patients) study was a prospective observational pilot study enrolling HF patients with Optivol-capable cardiac devices within 48 hours of a hospital admission characterized by worsening HF symptoms. The primary end point was the difference in times from admission to 50% improvement in impedance and to when patient was medically ready for discharge. The nonparametric sign test was used to determine if the difference was significant. A total of 20 subjects were enrolled over a 24-month period. The median ADHF length of stay was 7 days. Of the 20 subjects, 18 achieved the intrathoracic impedance improvement threshold before discharge. The time to reach the threshold for improvement was 2.5 days (interquartile range 2.0-6.0). The difference between days to 50% impedance and days to provider's discharge decision was 3.0 (P = .0072). CONCLUSIONS: Intrathoracic impedance changes were evident over a short duration in the majority of patients admitted for ADHF and may be a potential criterion for discharge readiness.