5. Mitral regurgitation
The human heart consists of four chambers: two atria and two ventricles. Blood coming from the lungs enters the left atrium first, then passes to the left ventricle to be transported to the body. Between the left atrium and the left ventricle lies the mitral valve. Under normal conditions, this valve prevents blood from leaking back into the left atrium. When diseased or injured, the mitral valve cannot prevent the retrograde flow of blood from the left ventricle into the left atrium. Thus, the left atrium starts filling with blood, and this increases the blood volume that is transported to the left ventricle. The resulting heart failure causes flash pulmonary edema.