Light micrograph section through human heart tissue showing myocardial fibrosis. This condition arises when the heart's fibroblasts produce collagenous scar tissue. It is defined by a significant increase in the collagen volume of myocardial tissue. The process is complex and involves all components of the myocardial tissue and can be triggered by tissue injury from myocardial ischemia (hypoxia), inflammation and hypertensive overload.