Heart sound is a highly nonstationary signal, and the Short-time Fourier Transform ation(STFT) is an effective method for this kind of signal to be analysed. Because of the nonstationarity of the phonocardiogram, it is important to maintain an analysing time window as short as possible to guaranty the stationarity hypothesis over small analysed segments. This will reduce the frequency resolution of the resulting spectrogram. However by adjusting the sliding time window, we can reach an acceptable result. The spectrogram is caculated by using first, short length sliding window to generate a temporal representation of the PCG, then longer length sliding window in order to generate a spectral representation of the PCG power. The resolution in such representations depend directly on the sliding window length. The temporal representation allows heart sounds and cardiac cycle durations to be measured. Whereas the spectrum, assuming a good frequency resolution, allows spectral characterization of each heart sound. The results we obtained on normal PCG signal show that the STFT analysis with different scale basis provides a clear comprehension of the cardiac events in both time and frequency domain.