A new mouse cardiac electrophysiology method was used to study mice harboring an 
alpha-myosin heavy chain Arg403Gln missense mutation (alpha-MHC403/+), which 
results in histological and hemodynamic abnormalities characteristic of familial 
hypertrophic cardiomyopathy (FHC) and sudden death of uncertain etiology during 
exercise. Wild-type animals had completely normal cardiac electrophysiology. In 
contrast, FHC mice demonstrated (a) electrocardiographic abnormalities including 
prolonged repolarization intervals and rightward axis; (b) electrophysiological 
abnormalities including heterogeneous ventricular conduction properties and 
prolonged sinus node recovery time; and (c) inducible ventricular ectopy. These 
data identify distinct electrophysiologic abnormalities in FHC mice with a 
specific alpha-myosin mutation, and also validate a novel method to explore in 
vivo the relationship between specific genotypes and their electrophysiologic 
phenotypes.