Pulsus paradoxus is characteristically seen in cardiac tamponade. Absence of pulsus paradoxus is seen when cardiac tamponade is associated with all except one

Mechanism of pulsus paradoxus: Inspiration → increased RV filling and decreased LV filling → left shift of IVS → LV compression and decreased systolic arterial pressure. Pulsus paradoxus  is absent  when cardiac tamponade occurs in a condition which permits equal filling of both ventricles or more filling of LV. ASD= equal filling of both ventricles in both phases of respiration. VSD=free communication between ventricles preventing differential filling. AR= filling of LV is maintained irrespective of respiration