In unaffected individuals, the chambers of the left side of the heart are under higher pressure than the chambers of the right side because the left ventricle has to produce enough pressure to pump blood throughout the entire body, while the right ventricle needs only to produce enough pressure to pump blood to the lungs. In the case of a large<unk>  (> 9 mm), which may result in a clinically remarkable left-to-right shunt, blood shunts from the left atrium to the right atrium. This extra blood from the left atrium may cause a volume overload of both the right atrium and the right ventricle. If untreated, this condition can result in enlargement of the right side of the heart and ultimately heart failure. Any process that increases the pressure in the left ventricle can cause worsening of the left-to-right shunt. This includes hypertension, which increases the pressure that the left ventricle has to generate to open the aortic valve during ventricular systole, and coronary artery disease which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular diastole. The left-to-right shunt increases the filling pressure of the right heart (preload) and forces the right ventricle to pump out more blood than the left ventricle. This constant overloading of the right side of the heart causes an overload of the entire pulmonary vasculature. Eventually, pulmonary hypertension may develop. The pulmonary hypertension will cause the right ventricle to face increased afterload. The right ventricle is forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to right ventricular failure (dilatation and decreased systolic function of the right ventricle). If the<unk>  is left uncorrected, the pulmonary hypertension progresses and the pressure in the right side of the heart becomes greater than the left side of the heart. This reversal of the pressure gradient across the<unk>  causes the shunt to reverse - a right-to-left shunt. This phenomenon is known as Eisenmenger's syndrome. Once right-to-left shunting occurs, a portion of the oxygen-poor blood gets shunted to the left side of the heart and ejected to the peripheral vascular system. This causes signs of cyanosis. Image:Gray468.Heart of human embryo of about 35 days Image:Atrial septal defect-en.Atrial septal defect with left-to-right shunt File:Blausen 0069<unk> SeptalDefect 02.Illustration depicting<unk>
Atrial septal defect
Atrioventricular septal defect
Heart septal defect
Ventricular septal defect
Aortopulmonary septal defect
Tricuspid atresia
Persistent truncus arteriosus
Double inlet left ventricle