A new estimator, Bandwidth Imaging, related to the bandwidth of the ultrasound Doppler signal is proposed as a classification function of blood and tissue signal in transthoracial echocardiography of the left ventricle. An in vivo experiment is presented, where the apparent error rate of Bandwidth Imaging is compared with the apparent error rate of Second-Harmonic Imaging on 15 healthy men. The apparent error rates are calculated from the 16 myocardial wall segments defined in . A hypothesis test of Bandwidth Imaging having lower apparent error rate than Second-Harmonic Imaging is proved for a p-value of 0.94 in 3 segments in end diastole and in 1 segment in end systole. When data was averaged by a structural element of 5 radial, 3 lateral and 4 temporal samples the numbers of segments increased to 9 in end diastole and to 6 in end systole. This experiment indicates that Bandwidth Imaging can supply additional information for automatic border detection routines on endocardium.