Aiming at Ambient noise cancellation for electronic stethoscope used in noisy hospital and ambulance, this paper proposes a two-mic sound enhancement algorithm based on CASA. The algorithm manages to segregate target heart sound from ambient noise using cues such as interaural intensity difference(IID) and auditory masking effect. Just like adaptive algorithm, it is useful to almost all kinds of noise. And experiment results show that CASA can increase signal noise ratio(SNR) by 10db more than NLMS.