Heritability of premature mitral valve disease in Cavalier King Charles spaniels

Mixed model analysis of 1252 records of cardiac auscultation of 4- to 5-year-old Cavalier King Charles spaniels (CKCS) from 1991 to 2008 in conjunction with the Kennel Club pedigree records of all dogs registered from the mid 1980s to September 2007 was used to estimate variance parameters of premature mitral valve disease (MVD). Data were limited to dogs ⩾4 and <5 years of age to ensure diagnostic distinction between early and late onset MVD. Cardiac murmurs were detected in 108/1252 (8.6%) dogs. Heritability estimates of 0.67 (standard error, SE 0.071) for the grade of murmur and 0.33 (SE 0.072) for the presence/absence of murmur were calculated. The variance due to clinician was 0.02 (SE 0.012) for grade and 0.03 (SE 0.017) for presence/absence of murmur. These results indicate that the presence and severity of MVD, as assessed by cardiac auscultation, in 4- to 5-year-old CKCS is highly heritable and that selection against the disease should be successful.