The heart sounds lub and dup occur when the atria contract and subsequently when the ventricles contract.?

The heart sounds "lub" and "dup" correspond to the closure of heart valves during the cardiac cycle, not directly to atrial and ventricular contractions. The "lub" (S1 sound) occurs when the atrioventricular (AV) valves close at the start of ventricular contraction (systole), while the "dup" (S2 sound) occurs when the semilunar valves close at the end of ventricular contraction. Therefore, these sounds represent the heart's valve function rather than the contractions themselves.