Heart stents are devices used to open up blockages of the arteries supplying the heart muscle. Modern day stents are extremely safe but there are several important issues that can arise with stents that may lead to complications. When stents fail, this often happens when excess scar tissue builds up inside the stent causing the artery to become narrowed again (called stent restenosis) or if the stent fills with blood clot, this can cause an acute heart attack (called stent thrombosis). Here Professor Barlis provides an overview of some of the reasons that may lead to stent restenosis or thrombosis.