The structure and components of the atrial chambers.

We discuss the implications of accurate knowledge of the human atrial chambers for those seeking to model atrial structure, and correlate the muscular activity with electrical signals. We stress first the importance of describing atrial components in attitudinally appropriate fashion, a feature sadly ignored by generations of morphologists. When considered relative to the body, the right atrium is positioned anteriorly relative to its alleged left-sided counterpart. We then described how each atrium possesses a venous component, an appendage, a vestibule, these parts being supported by the body of the atrium, and how the two chambers are separated by the septum. We extend this information by describing the detailed structure of each atrium, and then emphasise that it is only the floor of the oval fossa, and its antero-inferior rim, that are true septal structures. The so-called 'septum secundum' is the superior interatrial fold. Emphasis is then given to the muscular connections between the atriums, these unions obviously underscoring the potential for interatrial conduction. We then continue by discussing the structure of the atrial walls, which vary markedly in their thickness. It is the alignment of the myocytes within these walls that determines the velocity of conduction through them. In this setting, we also discuss the morphological features that distinguish between working myocytes and the myocytes of the conduction system, stressing the importance of rules established almost 100 years ago.