A specific mutation that causes HCM is seen in Maine Coons for which testing services are offered. Of all the Maine Coons tested for the MyBPC mutation at the Veterinary Cardiac Genetics Lab at the College of Veterinary Medicine at Washington State University, approximately one-third tested positive. Not all cats that test positive will have clinical signs of the disease, and some Maine Coon cats with clinical evidence of hypertrophic cardiomyopathy test negative for this mutation, strongly suggesting that a second mutation exists in the breed. The HCM prevalence was found to be 10.1% (95% CI 5.8 -14.3% ) in this study. Early growth and nutrition, larger body size, and obesity may be environmental modifiers of genetic predisposition to HCM.