I've had nine heart procedures over the years, including stents. However, one time, I experienced the symptoms of a heart attack, but when they did the angiogram, the blockage went away. I was diagnosed with a "coronary artery spasm". Do a google search on it, and you'll find out how serious they can be, even fatal if not taken care of. Mine was caused by an electrolyte imbalance, but smoking can also cause them. I'm not a doctor, and in no way can you be certain it was a coronary artery spasm, but if it was, it's serious and he needs to take control of his health.