I am considering going off birth control pills after having been on them for more than 11 years. What effect will this have on my body? Are there any side effects? I am 43, severely overweight and have high blood pressure. I am especially concerned that going off the Pill will cause changes in the regularity, length and heaviness of my periods.

After being on the pill for 11 years, you can certainly expect some changes when you stop. Your periods may take several months to return on their own, or your cycles may be irregular. Cramps may be worse in non-pill cycles and blood flow may be heavier. As you are in your early 40s, you may be entering perimenopause at some time in the near future, and going off the pill may produce more symptoms than it would have when you were younger; the pill may have been masking such symptoms of the perimenopause as irregular cycles, mood changes and hot flashes.
Because of your high blood pressure, the pill is probably not the best contraceptive or hormone-regulating choice for you; you are at increased risk for cardiovascular complications like stroke and heart attack. I would advise you to stop the pill and monitor your symptoms and blood pressure. If you begin to have terrible problems with your cycle, you may want to explore options with your doctor such as progesterone supplementation, hormone replacement therapy or even resuming a low-dose birth control pill if it does not raise your blood pressure. Irregular cycles are a part of life in the perimenopause. If you have not entered that phase of your life yet, going off the pill may cause a temporary "hiccup" in your cycles or absolutely no changes at all -- you just have to wait and see what happens with you.