What Causes Rapid Heart Rate During Intercourse And Premature Ejaculation?

i am 37 yrs and have a history of hypertension and i have been on these medication(altacand and aprinox) for 2yrs. i have noticed most frequently that any time i am about to have sex with my wife , my heart beat goes up very rapidly, am tensed and the fear of loosing my erection is always there. i loose my erection very quickly and i have notice that even in the face of sexually stimulating scenes, this does not trigger any arousal in me. am beginning to feel impotent, i am doubting my abililty to satisfy a woman sexually and that has began to affect my mood.. am depressed and sad. i used to be a stud but i do not understand what is going on here.. pls help me....