We found that (1) the H3R is expressed in the mouse LV; (2) isolated cardiac fibroblasts possess the H3R, which was up-regulated in response to Ang II; (3) blockade of the H3R with A331440 did not alter cardiac fibrosis or inflammation; and (4) activation of the H3R with imetit significantly reduced cardiac fibrosis and macrophage infiltration. The gene discussed is HRH3; the disease is fibrosis.