Well the term “stent failure” usually indicates either that renarrowing has occurred or that it has been blocked completely.
Complete blockage can be sudden and obviously causes chest pain, breathlessness or sweating, chest discomfort and may include all the features of a heart attack.
Re-narrowing on the other hand, usually occurs slowly over time and is marked by return of symptoms such as chest pain or breathlessness on walking. In fact, any of the symptoms you had before the heart stent was inserted can return.
Some cardiologist do perform routine tests like a treadmill stress test after insertion of heart stents while others would monitor for symptoms with regular followup in the heart clinic.