In canine heart failure induced by rapid right ventricular pacing, the number of chymase-positive mast cells increased in the left ventricle compared with the normal group; however, a chymase inhibitor significantly decreased chymase-positive mast cell density, cardiac angiotensin II concentration, mRNA levels of TGF-β, collagen I, and collagen III, and cardiac fibrosis [30]. The gene discussed is CMA1; the disease is heart failure.