How long do stents do what they do?

Over the past 7 years I have had a total of 10 cardiac stents implanted around my heart. The most recent in April when I received 3. After the follow up visit with my Dr. I asked how long stents last. He replied that they should last the rest of my life. While driving home it dawned on me that his answer could be taken in different ways. If I had a heart attack and died tomorrow he would be right, they lasted for the rest of my life. Anybody have a more precise answer?