Myoglobin (symbol Mb or MB) is an and binding found in the cardiac and of vertebrates in general and in almost all mammalsMyoglobin is distantly related to . Compared to , myoglobin has a higher affinity for oxygen and does not have with oxygen like hemoglobin does In humans, myoglobin is only found in the bloodstream after
High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin. Myoglobin is found in Type I muscle, Type II A, and Type II B; although many texts consider myoglobin not to be found in, this has proved erroneous: there is also myoglobin in smooth muscle cells.