An example of hot active region loop oscillations observed by SUMER and SXT is presented. The hypothesis that a fundamental mode standing slow sausage (acoustic) wave is initiated by a footpoint microfiare is tested and confirmed using a forward modeling approach. The oscillation is set up immediately after the heating pulse. The duration, temporal behavior, and total heat input of the microflare are estimated using the oscillation parameters. The rapid energy release is followed by cooling. The time-distance profile of the heating rate along the loop is recovered using the intensity and Doppler-shift time series. Hot loop oscillations are mainly observed in the Doppler shift. The absence of intensity oscillations in this and similar cases is explained. It is also found that the intensity oscillation, unlike the Doppler shift oscillation, undergoes half a period phase variation when the background intensity passes through its maximum, thus making it more difficult to detect.