A hazardous materials placard is a diamond-shaped sign that must be affixed to any motor vehicle that carries hazardous materials. Ordinarily, it has a four digit number in the middle of the placard and a one digit number at the bottom that shows the hazard class and specific material being carried.
Aortic stenosis is abnormal narrowing of the aortic valve. A number of conditions cause disease resulting in narrowing of the aortic valve. When the degree of narrowing becomes significant enough to impede the flow of blood from the left ventricle to the arteries, heart problems develop. The oxygenated blood then returns to the left atrium and passes through the mitral valve into the left ventricle. 2  Blood is pumped by the left ventricle across the aortic valve into the aorta and the arteries of the body.
Causes. The aortic valve allows oxygen-rich blood to flow from the heart to the aorta. It prevents the blood from flowing back from the aorta into the heart when the pumping chamber relaxes. Bicuspid aortic valve is present at birth (congenital).