Because myocyte dysfunction and disarray are early abnormalities in hypertrophic cardiomyopathy (HC), we tested if Doppler myocardial imaging (DMI) could identify systolic and diastolic dysfunction in mutation carriers (MC) (genotype positive patients without hypertrophy, defined as phenotype negative after conventional screening tests). In a single family with a missense mutation in the myosin binding protein C gene (Arg 502 Gln) we identified 5 MCs; these subjects were asymptomatic and had normal physical examination, normal electrocardiogram, treadmill stress test, ambulatory Holter electrocardiogram, and normal conventional M-mode, 2-dimensional, and Doppler echocardiography. In each patient we performed a DMI study and measured the peak velocities of the systolic (S), rapid filling (E), and atrial contraction (A) waves in the 4 sides of the mitral annulus, in 8 left ventricular segments (apical views), in the tricuspid annulus, and in 2 right ventricular segments. These data were compared with those from 10 normal volunteers matched for sex, age, and body surface. Compared with the normal volunteers, the MCs had lower left ventricular systolic velocities and higher right ventricular systolic velocities; lower diastolic rapid filling velocities; higher or similar atrial contraction velocities; reduced E/A; lower percentage of annular sides and segments with E/A >1 and lower average number of sides and/or segments with E/A >1 per patient; similar right ventricular rapid filling velocities; and similar or higher atrial contraction wave velocities. Thus, DMI detects important left and right ventricular annular and regional myocardial contraction and relaxation abnormalities independently of the presence of hypertrophy, in HC. These results show that DMI is more sensitive than conventional echocardiography and establishes a new and highly accurate method for the noninvasive screening of MCs of the disease.