Heart sound is a faint signal which is difficult to be acquired. This paper presents the methods for the heart sound acquisition used electret microphone,including the heart sound extraction project, principle, rules and the impedance conversion of microphone. In order to acquire the useful heart sound, the microphone is shielded by a special device. The clinical experiments have indicated that the first and second heart sound can be almost acquired by the microphone, but it is difficult for the third and fourth , which are affected by sex and bodily form.