This unique work presents one of the most significant organ failure condition - cardiocirculatory shock - and the prominent role of Methylene Blue (MB). Through their extensive experience, the authors' consider that the lifesaving feature of MB is still underestimated. For this reason they outline key concepts of MB, mentioning essential experimental data, yet focusing mainly on its application in the care of critically ill patients. In an easy-to-read format, the 18 chapters were organized in a didactically structured order, distributed in four parts. The first part introduces the general conceptual aspects and physiology of the endothelium. The second part presents the particularities of endothelial dysfunction in different types of shock. Methylene blue is discussed in detail in the third part. In the fourth part, particular situations of endothelial dysfunction, such as heart surgery and organ transplantation, are described. Additionally, the two complementary subjects of acid-base balance and the therapeutic use of inhaled nitric oxide are mentioned. Finally, looking for therapeutic alternatives for what we classify as "vasoplegic endothelial dysfunction", MB remains promising as an adjuvant to sympathomimetic amines. The combination of three recently proposed concepts may be useful in obtaining better results against the high mortality rates in critically ill patients. These three concepts are "wide-spectrum vasopressors", vasopressor economy strategies, and microcirculation protection against the harmful effects of using high concentrations of amines. This books translational approach will appeal to a variety of readers within the health specialties of medicine, biomedicine, physiotherapy, nursing, odontology, and basic science.