Why Does My Child Sometimes Feel His Heartbeat And Mild Pain In His Left Testicle For About 10 Seconds?

My 11 year old son just told me that sometimes he can feel his heart beat in his testicles. He said it lasts for about 10 seconds then goes away. He also said that when he feels the heart beat, his left testicle hurts a little. What could this be? Is this something he needs to see his doctor for right away?