Some BP medications can cause weight gain, but it's very rare. The stent would not cause this in any way. I too, was active (walking 6 miles a day), good diet, all you are, but developed a weight problem. I had all my meds evaluated for a side effect of weight gain, and none had this. I drastically changed my eating habits, and eat every 3 hours, small amounts of good stuff. I started doing this in Jan. and have lost 42 lbs.
If you are taking Coreg, which is a BP medication, there is a very good chance it is causing you to gain weight, it is a side effect that is common. It slows down the heart rate, the body isn't working as hard, the weight comes on. Other beta blockers do that as well. Like you, I had a healthy lifestyle with exercise, diet, etc but I put on a quick fifteen pounds when I started taking Coreg. However, I adjusted my exercise, diet, etc like mammo advised and the weight came off quickly. Also, be sure that you aren't gaining weight because of water retention, that's certainly a sign of heart trouble.
Blood pressure meds, as well as statins, can and do cause weight gain in some patients. It IS very common, especially when taking both.