What can I do to calm my nerves before an interview?

I am a very capable person? I am a manager where I work and I have many responsabilities. I work in retail so I deal with a large amount of people on a daily basis. I'm ready for a new career, something outside retail. I recently applied for a good job and had my interview last week. My interview was with a panal of five people, I was so nervous all I could here was my heartbeating in my ears! My answers did not reflect my capabilities AT ALL! needless to say I didn't get the job. I am not this person, I am usually calm and confident. How can I better prepare myself for my next interview? Now that this has happened I'm afraid I'll be that way next time!