Tonight I visited my favorite pub where I got onto a discussion with a new gun owner. He had just completed a self defense training course. He began to talk about trading for center mass aiming. I soon realized that he had a misconception about what it means to aim center mass. He thought it meant shooting to hit between the shoulders and waistband. I explained the he has a misconception. My Marine pistol training asserted that center mass a place in the center of the chest between the collar bones and the diaphragm. That is where the sternum sometimes called the breastbone. You can see that in the image. It is the perfect center mass target because it is close to the heart and lungs it is also in the area of the vena caves, a major vein that returns blood to the heart so it can be re-oxigenated. Add to that the positional relationship with the heart and lungs and it becomes a perfect target area. Hit the sternum and bone splinters can cut the vena caves, drive bone splinters into the heart and/or lungs and generally stop an assailant in his tracks with one shot from a.38 and larger. I train by printing of the included image so that it equivalent in size to the body side of a 5'10" person. My goal is to put as many rounds into the sternum as I can. Give it some thought understanding that the best self technique is to deliver crippling to fatal shot in the first moments of a gunfight.