I Usually Experience Sudden Increase Of My Heart Beat Which

I usually experience sudden increase of my heart beat which will then result to lost of erection during the very beginning of sex with my wife, this started few month back and I am 47 years old, please what could be the cause and what can I do to remedy the situation because it is really embarrassing to me. I don't mind getting reply through my email, ( YYYY@YYYY ). Thank for your anticipated assistance.