I am the largest blood vessel, artery, I am the inner layer of the artery, Endothelial layer, I lie in the middle of the chest, Heart, I appear if the valves of the veins isn't working fine ., Varicose veins, I am the outer layer of the artery, Connective Tissue, I exchange the important substances and wastes, Capillary, I carry the blood to the heart, Veins, I am the pacemaker of the heart, Sinoatrial node, I am a valve that moves the blood from the left ventricle to the aorta, Aortic valve, I am a valve that make the blood move from the right atrium to the right ventricle, Tricuspid valve

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