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