Medical Genetics Heart abnormalities represent the next most common category of defect common heart defects include holes in the heart where blood can pass from one side of the heart to the other. Again, these may not all be detected at birthMedical Genetics Heart abnormalities represent the next most common category of defect. Common heart defects include 'holes in the heart' where blood can pass from one side of the heart to the other. Again, these may not all be detected at birth