The heart consists of several types of distinct cells. These different types of cells can be categorized into two major categories: excitable and non-excitable cells. Excitable cells are cells that can generate action potentials and include cardiomyocytes, pacemaker cells, Purkinje cells, and smooth muscle cells. On the other hand non-excitable cells do not generate action potentials; they include fibroblasts, endothelial cells, and adipocites. These seven different types of cells constitute almost all of the heart mass; they trigger contractions, pump blood, and provide structure.