When you listen to your heart using a stethoscope or you listen to someone else heart by placing your head on their chest or by using a stethoscope, you will hear two sounds during each heart beat : a lub-dub lub-dub sound. This sound is created by valves closing on the blood inside the heart. These valves purpose is to prevent blood from flowing backward in any of the four chambers of the heart during the pumping of blood (contraction and relaxation of the heart). The first sound (the lub) happens when the mitral and tricuspid valves close. This happens when the pressure in the ventricles rises above the pressure in the atria, this cause valves to close inorder to prevent back flow of blood from the ventricles into the atria. The next sound (the dub) happens when the aortic and pulmonary valves close after the blood has been squeezed out of the heart. This happens when the left ventricle becomes empty, its pressure falls below the pressure in the aorta, and the aortic valve closes. Like wise, when the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonary valve closes. Thus, during each heart beat you will hear a lub-dub lub-dub sound.
Don't believe the above Essay! Didn't you ever wonder why they use the machine with the Paddles that Shocks your chest area on most 50 year olds ? It's because everyone needs to have their Batteries Re-Charged so the Electric Pump in your Chest will keep Pumping your Blood for many Years to come ! I hope the Original question was a JOKE!!! If not, I think I'll hang myself for FUN.