veins, arteries, capillaries... Arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood directly to the heart. I hope you guys are just hitting capillary beds when talking about all of this bleeding from injections. Going into a vein would give you a distinct 'flash' of blood when you aspirate, and you most definitely must aspirate. You wouldn't be able to hit an artery unless you are way the hell off and driving that needle with conviction. You'd also be in considerable pain, seeing as they are innervated (have nerves around them) and wrapped in musculature. Every vein is a direct pathway to your heart, then your lungs, then your heart, then potentially your brain. It's why junkies shoot up the way they do. Be careful, inject yourselves properly in the proper sites. FYI, IMHO...