septal defect

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septal defect (sep-t'l) n. a hole in the partition (septum) between the left and right halves of the heart. This congenital condition is due to an abnormality of heart development in the fetus. It may be found between the two atria (atrial s. d., ASD) or between the ventricles (ventricular s. d., VSD). A septal defect permits abnormal circulation of blood from the left side of the heart to the right, which results in excessive blood flow through the lungs. Pulmonary hypertension develops and heart failure may occur. Large defects are closed surgically or using percutaneous catheter techniques but small defects do not require treatment.