atrial ventricular canal defect

a·tri·al ven·tric·u·lar ca·nal de·fect

a defect caused by deficient or absent septal tissue immediately above and below the normal level of the atrioventricular valves, including the region normally occupied by the A-V septum in hearts with two ventricles. The A-V valves are abnormal to a varying degree.
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