We previously reported that chronic ischemic HF induced by coronary ligation results in an exacerbated pro-inflammatory cell profile in the systemic circulation, spleen, and failing heart. In addition, this pro-inflammatory cell profile was strongly influenced by the cardiosplenic axis; however, the role of this axis in other etiologies of HF is unknown. Immune cells infiltrate the heart early (1-4 weeks) after pressure-overload injury, but it is unknown whether these cells persist and are of pathological import during chronic pressure-overload HF. We hypothesized that phenotypic changes in mononuclear phagocytes are necessary for the transition from compensatory hypertrophy to chronic HF during sustained pressure-overload, and that inhibition of myocardial immune cell infiltration would ameliorate this progression. Pressure-overload was induced by transverse aortic constriction (TAC) in wild-type (WT) C57BL/6 mice, and in macrophage Fas-induced apoptosis (MAFIA) Tg mice, which allows ablation of c-fms expressing cells upon administration of the AP20187 dimerizer. Compared to sham mice, TAC mice developed progressive cardiac dysfunction beginning at 2 w with significantly (p<0.05) reduced LVEF (59 ± 10 vs 67 ± 3 %), increased left atrial size (2.29 ± 0.1 vs 2.04 ± 0.1 mm), and increased E/E’ Doppler ratio (31.8 ± 6 vs 24.0 ± 3). Circulating CD11b+Lineage- monocytes were elevated in TAC mice at 2 w (1.7 ± 0.2 vs 1.0 ± 0.1 %, p<0.05); however, these levels normalized by 8 w. Moreover, at 8 w, no significant differences in the levels of splenic and cardiac mononuclear phagocytes were seen between TAC and sham mice. Systemic ablation of mononuclear phagocytes beginning 2 w after TAC in MAFIA AP20187-treated mice did not rescue cardiac function or delay HF progression compared to TAC MAFIA vehicle-treated mice over the course of 16 w (LVEF 43 ± 18 vs 45 ± 18 %). We conclude that in contrast to chronic ischemic HF, inflammatory cell-mediated cardiac injury does not have primacy in chronic non-ischemic HF induced by pressure-overload. These findings highlight the importance of the index injury in regard to immune cell activation in HF, and suggest that therapeutic immunomodulatory approaches may not be equivalent across the various etiologies of this disease. Author Disclosures: B. Patel: None M. Ismahil: None M. Goel: None T. Hamid: None S. Bansal: None S.D. Prabhu: None.