atrioventricular , semilunar - When listening to the heart, the examiner listens for the unique lup-dup sounds of the heart to understand if the heart is healthy. These sounds are generated when the heart beats to allow blood to flow throughout the body. The sound is basically created each time the heart valves snap shut. The "lub" is the atrioventricular valves snapping shut and the "dup" sound occurs when the semilunar valves close at the end of systole.