Major differences among reptile taxa include the shape of the heart, degree of separation of the ventricular compartments, degree of development of the intraventricular muscular ridge, and in crocodilians, the interventricular septum. In many cases, the structural-functional features of the reptilian heart provide adaptive plasticity, allowing for the ecological and behavioral diversity seen. As a result, variation may surface in clinical measures of cardiac performance. This article updates clinical context, provides an understanding of the variation in reptilian cardiovascular systems, and their functional implications for the assessment and treatment of reptile patients.