Complications are minimal in the period immediately after the stenting procedure. There is, however, a small chance that stents will damage the vessel when implanted, sometimes causing a tear or dissection of the artery. However, statistics have shown that this generally does not affect long-term prognosis.

To prevent the formation of obstructing blood clots (subacute thrombosis), the physician will prescribe aspirin and other antiplatelet drugs (especially clopidogrel). Subacute thrombosis is a rare complication that occurs when platelets aggregate and form a blood clot within the stent, potentially causing closing of the stent and a heart attack. It can occur with both drug-eluting and bare metal stents. Studies have shown that the rate of this serious complication ranges from 0.5 percent to 3 percent, depending on the kind of stent used, the placement of the stent, the nature of the disease and the post-stent medical therapy. It may occur up to one year after the procedure. Thrombosis rates are roughly equal among bare metal and drug-eluting stents, providing that antiplatelet therapy is used for drug-eluting stents. If patients discontinue their antiplatelet therapy early, they raise the risk of suffering from thrombosis.

There is also a risk that the artery will re-narrow (restenose) within six months at the site of the stent implantation. The risk of restenosis, however, has been dramatically reduced as a result of the widespread use of drug-eluting stents, which are coated with special agents that improve the stent's incorporation into the wall of the artery. Currently, the restenosis rate for coronary arteries treated with drug-eluting stents is less than 10 percent. The risk of restenosis is increased in patients with diabetes and “high-risk” patients with acute coronary syndromes (e.g., heart attack).

If restenosis does occur, the physician may recommend repeat stenting. This decision is influenced by several factors, including the size of the coronary vessel. Research suggests that patients with large vessels (3 millimeters or greater) have a significantly lower rate of restenosis with repeat stenting, as compared to balloon angioplasty. For small vessels, research suggests balloon angioplasty is the preferred therapy. And still, depending on the degree of cardiac impairment, there are patients for whom coronary artery bypass surgery may be the preferred treatment to stenting.

Neglecting to alter controllable risk factors (e.g., smoking) can also affect the success rate of the stenting and any other catheter-based procedures (e.g., angioplasty).