This chapter describes the pathophysiology of the cardiovascular system as it applies to Emergency Medicine, and in particular the Primary FRCEM examination. The chapter outlines the key details of the control of blood pressure and heart rate, cardiac output, blood flow, cardiac cycle, ECG, pharmacological manipulation of the heart, shock, oxygen delivery and consumption, body fluid homeostasis, crystalloid solutions, colloidal solutions, and exudates and transudates. This chapter is laid out exactly following the RCEM syllabus, to allow easy reference and consolidation of learning.