Anxiety, with an increase in hea rate or decreasing venous return to the hea (standing), causes the click and murmur to occur earlier in systole (closer to S1). Lying down, squatting, sustained hand grip exercise, or passive leg lifting in the supine position increase venous return and cause the click and murmur to occur later in systole (less gravity and more venous return). The diagnosis is best made by echocardiography. -adrenergic blocking agents are frequently used for treatment of supraventricular tachycardias. Calcium channel blockers are also used in symptomatic cases. Ref - Harrison's internal medicine 20e pg 1821,1697