Giant&;a&;wave in JVP is seen in-

in Tricuspid stenosis The jugular veins are distended, and in patients with sinus rhythm there may be giant a waves. The v waves are less conspicuous, and because tricuspid obstruction impedes RA emptying during diastole, there is a slow y descent. In patients with sinus rhythm there may be prominent presystolic pulsations of the enlarged liver as well. ( Harrison&;s principle of internal medicine,18th edition,pg no.1946 )