Echocardiography is a widely-used modality for diagnosis of the heart. It enables observation of the shape of a heart and estimation of global heart function based on B-mode and M-mode imaging. Subsequently, methods for estimating myocardial strain and strain rate have been developed to evaluate regional heart function. Furthermore, it has been recently shown that measurements of transmural transition of myocardial contraction/relaxation and propagation of vibration caused by closure of a heart valve would be useful for evaluation of myocardial function and viscoelasticity. However, such measurements require a frame rate much higher than that achieved by conventional ultrasonic diagnostic equipment. In the present study, a method based on parallel receive beamforming using diverging waves in transmit was developed to achieve high-frame-rate echocardiography over 300 Hz. The spatial resolution of the proposed method was validated using fine nylon wires. Although the widths at half maxima of the point spread functions obtained by diverging waves were slightly larger than those obtained by conventional beamforming and parallel beamforming with plane waves, the point spread functions, which were very similar to that obtained by conventional beamforming could be realized by parallel beamforming with diverging beams and compounding. Furthermore, a heart of a 23-year-old healthy male was measured, and a frame rate of 316 Hz, which was much higher than that realized by conventional sector scanning of several tens of Hertz, was realized with a full lateral field of view of 90 degrees.