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.