**1. Introduction**

Univentricular patients in the stage of Fontan palliation have a higher perioperative risk than their counterparts with normal hearts.

The diagnosis and treatment of children with congenital heart disease (CHD) has improved significantly over the last decades. The incidence of CHD has remained stable; the natural history of the lesions and overall survival rate have also changed notably. Advances made in surgical procedures and techniques, in concert with improvements in diagnosis, anesthesia practices, intensive care, and medical treatments, have transformed many of these fatal lesions into manageable chronic conditions [1].

Many more of these patients are surviving with this physiology than could have been contemplated 30 years ago and nowadays they seek medical attention for other causes different from their cardiovascular conditions that require surgical noncardiac procedures.

A normal biventricular cardiovascular system consists of a double circuit, pulmonary and systemic, connected in series and powered by a double pump. Many complex cardiac malformations are characterized by the existence of only one functional ventricle. This single ventricle (SV) has to maintain both the systemic and the pulmonary circulations, which at birth are not connected in series but in parallel [2].

Regardless of the exact nature of the connections, the completed circulation is often described as one having a single energy source, the systemic ventricle [3].

The survival improvement of patients with univentricular physiology is due to the development of the staged palliation approach for complex congenital heart lesions not suitable for biventricular repair. The final Fontan stage results in the conversion of a parallel circulation, to a pulmonary and systemic circulation that is in series regardless of the underlying cardiac anatomy [2, 4]. Such lesions include hypoplastic left-heart syndrome (HLHS), tricuspid atresia, unbalanced atrioventricular septal defects, double-inlet left ventricle, double-outlet right ventricle, and some forms of heterotaxy syndrome [5].

The objective of this chapter is to provide anesthesiologists the conceptual aspects applicable to the preoperative evaluation and perioperative management of patients with the unique Fontan physiology.
