"Because all things in the body are connected to each other, it is very likely that as you control your breath, you will also cause your heart rate to slow down, and some of your muscular tension to abate too." - American Addictions Center
I imagine that you can think of a few instances where you get angry easily, and once we are angry, it is hard to shake or rid of that feeling. Anger typically manifests itself through muscle tension.
In order to help with the tense feeling of anger, first try relaxation techniques. One example of this would be to GENTLY roll your head toward one shoulder and then towards the other, and coordinate your head with your breathing. Repeat this technique carefully until you feel the muscles in your neck relax a little.
If this does not work, try progressive muscle relaxation. In this exercise, you are to tighten and tense the stressed muscles and count to ten slowly and then release them. If you feel any pain, be sure to release the muscle right away!