Given that DSP cardiomyopathy, including the Myh6-McmTamDspfl/fl mice, exhibit severe myocardial fibrosis, likely secondary to extensive cell death, the effects of deletion of the Mb21d1 gene on myocardial fibrosis were determined by measuring the collagen volume fraction (CVF) and immunostaining for collagen 1 (COL1A1) in the myocardium of the control and experimental mice (4, 8). The gene discussed is COL1A1; the disease is Myocardial fibrosis.