Long Exhales
Have been a calming technique I have used for years. Often my heartbeat will accelerate and stay there, but by breathing in deeply, and then more slowly, by far, breathing out, I can decrease my heartbeat.
The method also works well when auditions and other exciting, yet stressful, events occur make the heart rate increase.
I had never thought to use this technique as "preventative medicine"! Now, I will!