The treatment of critically ill patients has been largely based on a macrocirculatory model described by Dr. William Harvey in the 19th century with practically total disregard for the microcirculation, which had not been studied by the times of Dr. Harvey's description. Imagine that we are trying to show some foreign friends some aspects of American culture, and all we do is drive them along our interstate highways without ever taking an exit. American culture (people and institutions) resides in the city streets. How much of American culture are our friends going to learn? Nothing. The microcirculation is the people and institutions that reside in our city streets. So we need to exit the highways and see what is happening between the capillary lumen and the cellular mitochondrion. This book provides an exit off the highways by describing the most recent and salient basic research on aspects of the microcirculation, in addition to offering suggestions and new theories to stimulate thinking that, hopefully, would result in better care of our critically ill patients. This book can be read from beginning to end or by chapter. A bulleted summary precedes every chapter to help those readers who do not have much time. Although to find the fundamentals, you must go to the body of the chapter. Many unproven new theories are incorporated in this book to try to complete the cardiocirculatory puzzle. These are indicated by UNT and may end up being right or wrong. Most notable UNTs are the kissing channels; the black hole theory of interstitial O2 transport; the redefinition of interstitium; the interstitial mechanism of blood flow regulation; the pressurization of clover leaves; the suggestion that shock and coma are our friends; the resistance of the brainstem to hypoxia; and the suggestion of an all-in-one approach to the treatment of shock patients.