Objectives: We hypothesized that some aspects of left ventricular assist device (LVAD) reverse remodeling could be independent of hemodynamic factors and would primarily depend upon normalization of neurohormonal milieu. Background: The relative contributions of LVAD-induced hemodynamic unloading (provided to the left ventricle [LV]) and normalized neurohormonal milieu (provided to LV and right ventricle [RV]) to reverse remodeling are not understood. Methods: Structural and functional characteristics were measured from hearts of 65 medically managed transplant patients (MED), 30 patients supported with an LVAD, and 5 nonfailing donor hearts not suitable for transplantation. Results: Compared with MED patients, diastolic pulmonary pressures trended lower (p < 0.01) and cardiac output higher (p < 0.001) in LVAD patients; V30 (ex vivo ventricular volume yielding 30 mm Hg, an index of ventricular size) in LVAD patients was decreased in the LV (p < 0.05) but did not change significantly in RV. The LVAD support improved force generation in response to beta-adrenergic stimulation in isolated LV (increase in developed force from 6.3 ± 0.6 to 18.5 ± 4.4 mN/m2, p < 0.01) and RV (increase in developed force, from 10.9 ± 2.0 to 20.5 ± 3.1 mN/m2, p < 0.05) trabeculae. The LVAD patients had higher myocardial beta-adrenergic receptor density in LV (p < 0.01) and RV (p < 0.01). Protein kinase A (PKA) hyperphosphorylation of the ryanodine receptor 2 (RyR2)/calcium release channel was significantly reduced by LVAD in both RV and LV (p < 0.01). Conclusions: Improved beta-adrenergic responsiveness, normalization of the RyR2 PKA phosphorylation, and increased beta-adrenergic receptor density in LV and RV after LVAD support suggest a primary role of neurohormonal environment in determining reverse remodeling of the beta-adrenergic pathway. © 2005 by the American College of Cardiology Foundation.