If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the occluded coronary artery die (chiefly through necrosis) and do not grow back. A collagen scar forms in their place. Recent studies indicate that another form of cell death, apoptosis, also plays a role in the process of tissue damage following an MI. As a result, the person's heart will be permanently damaged. This myocardial scarring also puts the person at risk for potentially life-threatening abnormal heart rhythms (arrhythmias), and may result in the formation of a ventricular aneurysm that can rupture with catastrophic consequences.