Genetically-manipulated mice harboring an alpha-myosin heavy chain Arg403Gln 
missense mutation (alpha-MHC403/+) display a phenotype characteristic of 
familial hypertrophic cardiomyopathy (FHC). Male and female (30 +/- 8 week old) 
heterozygous alpha-MHC403/+ mice and litter-mate controls were evaluated using a 
surface electrocardiogram (ECG) and an in vivo cardiac electrophysiology study 
(EPS). Wild type animals had normal intracardiac electrophysiology, with no 
significant differences between male and female control mice during EPS. The 
female wild-type mice did have slower heart rates and longer ECG intervals than 
their male wild-type counterparts. The female alpha-MHC403/+ mice had similar 
ECG's, cardiac conduction times, and refractory periods compared with female 
wild-type mice. In contrast, male FHC mice had distinctive ECG and 
electrophysiologic abnormalities including right axis deviation, prolonged 
ventricular repolarization and prolonged sinus node recovery times. During 
programmed ventricular stimulation, 62% of male alpha-MHC403/+ mice and 28% of 
female alpha-MHC403/+ mice had inducible ventricular tachycardia. These studies 
identify gender-specific electrophysiologic abnormalities in alpha-MHC403/+ FHC 
mice, concordant with the histological and hemodynamic derangements previously 
reported.