Believe it or not, non-steroid using individuals may experience heart muscle growth through rigorous exercise (such as aerobics). Steroid users differ in that the more they use and the longer they use, the more potential there is for growth. Negative side effects may not surface unless abuse becomes the norm, but it is best not to take the chance. Additionally, consistent steroid users may experience a decrease in the size of the heart muscles when they stop using. This essentially means that the heart starts to shrink. Again, past use/habits are likely to influence the level of change.
The hormone is synthesized and secreted from alpha cells (α-cells) of the islets of Langerhans , which are located in the endocrine portion of the pancreas. Production, which is otherwise freerunning, is suppressed/regulated by insulin from the adjacent beta cells. When blood sugar drops, insulin production drops and more glucagon is produced  In rodents, the alpha cells are located in the outer rim of the islet. Human islet structure is much less segregated, and alpha cells are distributed throughout the islet in close proximity to beta cells. Glucagon is also produced by alpha cells in the stomach.