In the present book we use echocardiography to explore the problematic of the cardiovascular effects of fasting - a recurring theme in Anaesthesiology. We assess whether it leads to fluid depletion and how much of an effect that has on the individual's position on the Frank-Starling curve. Subsequently, we set out to define the most reliable echocardiographic variables to assess fluid responsiveness in spontaneously breathing individuals, while also addressing the peculiarities of both goal-directed therapy and the anaesthetic state.