" Congenital disease can warp the heart with great variety. Valves can be sealed tight, missing parts—or absent altogether. Major vessels can be misplaced, narrowed, or blocked completely. A chamber can be too small or missing, a wall too thick or thin. The heart’s electrical system—its nerves—may go haywire. The muscle can be weak. Holes may occur almost anywhere, in almost any size. Studying heart pathology, one is reminded that the genetic symphony that produces a normal baby is indeed a wondrous and delicate one. "