If, and I stress if, a person was experiencing anxiousness caused by impending heart attack or circulatory issues; would exercise make it better/ wors?

Worse. If one is actually having circulation problems to any muscle, including the heart, then exercising those muscles will require more oxygen due to more work. This will, in turn lead to less oxygen to the organ than it would when at rest. So, if you are concerned you may having heart pain or circulatory insufficiency, see doc immediately.
Hard to say because. This is hard to answer because generally an impending heart attack does not cause anxiety; most heart attacks come out of the blue with no preceding anxiety. If someone was anxious i would not take it as a sign of impending heart attack, but if they're concerned about it i would advise having a cardiac stress test. If that's ok then exercise is one of the very best ways to reduce anxiety.