Restenosis is the recurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. Restenosis usually pertains to an artery or other large blood vessel that has become narrowed, received treatment to clear the blockage and subsequently become renarrowed. This is usually restenosis of an artery, or other blood vessel, or possibly a vessel within an organ.

Restenosis is a common adverse event of endovascular procedures. Procedures frequently used to treat the vascular damage from atherosclerosis and related narrowing and renarrowing (restenosis) of blood vessels include vascular surgery, cardiac surgery, and angioplasty.

When a stent is used and restenosis occurs, this is called in-stent restenosis or ISR. If it occurs following balloon angioplasty, this is called post-angioplasty restenosis or PARS. The diagnostic threshold for restenosis in both ISR or PARS is ≥50% stenosis.

If restenosis occurs after a procedure, follow-up imaging is not the only way to initially detect compromised blood flow. Symptoms may also suggest or signal restenosis, but this should be confirmed by imaging. For instance, a coronary stent patient who develops restenosis may experience recurrent chest pain (angina) or have a minor or major heart attack (myocardial infarction), though they may not report it. This is why it is important that a patient comply with follow-up screenings and the clinician follows through with a thorough clinical assessment. But it is also important to note that not all cases of restenosis lead to clinical symptoms, nor are they asymptomatic.