WORCESTER — The Worcester Regional Chamber of Commerce is getting to the heart of the matter concerning the Heart of the Commonwealth. "Worcester. A city with heart, history and promise," says the narrator at the start of a 30-second TV commercial extolling many attributes of Worcester that the chamber will run in markets including Boston, Providence and Springfield beginning Monday morning. "We think it's an investment that helps the region in a variety of ways," said Timothy P. Murray, president and CEO of the Worcester Regional Chamber of Commerce, about its TV advertising blitz initially planned to run from Monday until May 12.