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Although there are over 7000 different congenital cardiac defects,1 there are only a very few ways that a newborn or infant presents with cardiac disease. Symptomatic heart disease occurs in about 40% of congenital lesions, so that many infants present without symptoms. For this reason, perhaps, many clinicians consider the presence of a murmur as the most definitive evidence of heart disease. Unfortunately, this is the source of a very large number of unnecessary referrals to the pediatric cardiologist—the vast majority of murmurs occur in patients with normal hearts, and most innocent murmurs are misdiagnosed.2 Up to 50% of normal children present with an innocent murmur at some time, whereas only about 50% of newborns with symptomatic heart disease have murmurs on clinical presentation. Even assuming that all of the children without symptoms who have congenital heart disease have murmurs, this would make the presence of a murmur to be about 2% specific and 80% sensitive in the diagnosis of heart disease. There is no other sign in medicine that has such poor specificity and sensitivity yet is used with such certainty.

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Rather than asymptomatic heart disease, it is of utmost importance for the pediatrician to be able to quickly diagnose symptomatic heart disease. The change from a fetal circulatory system to a transitional circulation occurs immediately at birth, and the mature circulation develops within weeks.3 Because of these dramatic alterations in blood flow and oxygen uptake patterns in the neonatal period, the fetus with a stable cardiovascular status can become a newborn with severe cardiovascular symptoms, potentially leading to death, soon after birth. On the other hand, advances over the last few decades have given the clinician the tools to rapidly stabilize these critically ill neonates, and subsequently correct or ameliorate even the most complex defects. Thus, it is essential that the pediatrician be able to recognize the infant with symptomatic heart disease quickly, so that the appropriate diagnostic and therapeutic interventions can be initiated as soon as possible. Many pediatricians are insecure in their ability to recognize symptoms of heart disease, and thus fall back on the murmur as their gold standard of diagnosis, which can lead to devastating consequences for those symptomatic infants without murmurs. It is possible to overcome this insecurity by recognizing that there are only 3 different, overlapping, modes of presentation of symptomatic heart disease in the newborn and infant, each very easy to recognize during a routine examination. These modes of presentation are cyanosis, decreased systemic perfusion (hypoperfusion), and respiratory distress/failure to thrive.

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Prior to considering the modes of presentation of symptomatic heart disease in the newborn, it is worthwhile to review fetal physiology, to understand why symptomatic heart disease is rare in the fetus.

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Fetal Physiology

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Most of our knowledge of the fetal circulation presented in this section is derived from research in fetal sheep,4 but more recent studies in human fetuses ...

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