Yes, coronary stents are kosher. In fact they are a miraculous invention.
What are they? Wikipedia says: "A coronary stent is a tube placed in the coronary arteries that supply the heart, to keep the arteries open in the treatment of coronary heart disease. It is used in a procedure called percutaneous coronary intervention (PCI). Stents reduce chest pain and have been shown to improve survivability in the event of an acute myocardial infarction."
The coronary stent was invented by Julio Palmaz. The stainless steel, insertable mesh stent is expanded once inside the body to hold an artery open and allow blood to flow more freely. Palmaz secured funding for the development of the stent from restaurant owner Phil Romano (Fuddruckers and The Macaroni Grill). Palmaz co-developed the stent with Dr. Richard Schatz, a cardiologist at the time at the Brooke Army Medical Center. We would guess that Schatz is Jewish. They patented their invention in 1985.
The coronary stent is one of the greatest inventions of our time. The stent can be inserted through a small puncture in the groin or wrist and via balloon angioplasty it can open up quickly and with little to no pain a 99% occluded major coronary artery. The procedure takes about an hour and the patient is ambulatory after four hours and can resume many of his favorite activities :-) within one day.
To a person (like me) with CAD this rapid and amazing restoration of a person's quality of life is a true medical miracle of our times.