'a'wave in JVP is seen in-
The a wave is due to atrial systole.some blood regurgitates into great veins when the atria contract.In addition,venous flow stops, the resultant rise in venous pressure contributes to a wave. (Ganong&;s Reviw of medical physiology,23rd edition,pg no.512)
C.V.S
Will be large when atria contracts against resistance
Filling of ventricles
It is followed by "V" waves
in inspiration
Will be large when atria contracts against resistance