Physiology is the science that is applied at the boundary between life and death; this is why it's so important to those of us who tread that same boundary every day in the practice of anesthesiology and critical care. The functional difference between a patient who has just died and one who is still alive is physiology. What the heart, lungs, and circulation do in life is best understood through some simple, unifying principles of mechanics and chemistry. But that is not enough. There is also a way of thinking about these concepts that helps pull them together. Interestingly, that form of logic is almost identical to the way our brains work when we are solving logic puzzles. To that effect, brain teasers are included at the end of each chapter.