Animales Exoticos

Normal Reptile
Hear t Morpholo gy
and Function
Jeanette Wyneken, PhD
KEYWORDS

 Myocardium  Ventricle  Atrium  Cardiac  Muscular ridge
 Cavum arteriosum  Cavum venosum  Vacum pulmonale

Reptile hearts are simple in their external gross morphology but are complex internally.
The reptilian heart structure that is often described to introductory biology students is
deceptivelysimple because of the conceptual framework in which it is presented.
Even today, organ systems are described erroneously as though representing steps
in a linear progression from simple to increasingly complex and sophisticated vertebrates. In this stepwise linear framework, the relatively simple tubular fish heart is at
the base, the four-chambered mammalian heart is at the top, and the hearts ofamphibians (three chambers) and reptiles (three chambers, with a complex ventricle)
form other steps. Such an orderly sequential perspective dates back to Aristotle, who
tried to understand the complexity of organisms by arranging them hierarchically as
a ‘‘Ladder of Life’’ (scala naturae) based on structure. Such views of morphological
diversity ignore the branching and tree-like historiesof organisms. The diversity of
vertebrate heart forms, including those found in reptiles, are best viewed in the context
of diverse and nonlinear histories with many different branches.
Reptilian heart anatomy varies around a few major structural patterns. Although
each design appears grossly to have two atria and a single ventricle, there is much
more to this system, which reflects thephysiological demands and lifestyles of the
animals. In many cases, structural-functional features of the reptilian heart clearly
are adaptive to the ecology and behavior of the species. It is the structure of the
systems that provides the functional plasticity. The circulatory and respiratory
systems are structurally and functionally related in all vertebrates and are often
discussed together asthe cardiopulmonary system. This review focuses on the heart
and great vessels (cardiovascular anatomy), however, and omits the peripheral circulation and the pulmonary components.

Department of Biological Sciences, 266 Building 01, Sanson Science, Florida Atlantic University,
777 Glades Road, Boca Raton, FL 33431–0991 USA
E-mail address: jwyneken@fau.edu
Vet Clin Exot Anim 12 (2009) 51–63doi:10.1016/j.cvex.2008.08.001
vetexotic.theclinics.com
1094-9194/08/$ – see front matter ª 2009 Elsevier Inc. All rights reserved.

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Wyneken
COMPARATIVE HEART SHAPE, SIZE, AND LOCATION

The hearts of snakes are elongate, whereas those of chelonians, crocodilians, lizards,
and tuataras tend to be more ovoid or triangular in shape (Figs. 1 and 2). Heart mass is
0.20% to 0.32% ofbody mass in reptiles, with proportionately larger hearts found in
more athletic species and in climbing snakes.1
The location of the heart varies within reptilian lineages and even within taxa,
although the heart tends to be positioned roughly along the axial midline. In chelonians, part of the heart is often deep to margins of the humeral and pectoral scutes;
however, in some species, it ispositioned more posteriorly along the midline between
humeral-pectoral and pectoral-abdominal scute lines.2 In soft-shelled turtles (Trionychidae), the heart is displaced to the right.1 The shoulder girdles provide good landmarks in radiographs; the heart is typically just caudal to the level of the acromion
processes and cranial to the distal procoracoid process–procoracoid cartilage
junction.In lizards, the heart position may approach the gular regions (geckos of the genus
Hemidactylus1 and bearded dragons [Pogona vitticeps]) or may occur more caudally
within the rib cage (chameleons, iguanas, and varanids). In adult or large immature
iguanid and varanid lizards, the caudal portion of the ventricle is aligned with the elbow
when the arms are retracted against the body. In younger...