Partial AV Canal  (aka Incomplete AV canal)

The term partial AV canal generally refers to endocardial cushion defect, which have an interatrial communication but lack an interventricular communication. In these types of defects, the right and left atrioventricular valve annuli are divided into two distinct valve. A partial AV canal consists of a primum atrial septal defect and cleft of the left atrioventricular (mitral) valve leaflet.  Overall, the hemodynamic effect is one of a left to right shunt at the atrial level (which over time can cause right atrial and right ventricular dilation which depends on the size of the atrial shunt) as well as a left AV valve which has a varying degree of regurgitation depending on the size of the cleft. 

Image above used with permission from Texas Children's Hospital and courtesy of the division of cardiothoracic surgery