Dyspnea in a 52-Year-Old Woman

Shortness of breath has been going on for three months, but it sounds like it started pretty acutely three months ago. It was hard for me to say it's clearly progressed from somebody who had no clear exercise and tolerance to incapacitating the tolerance. So at very least it's been sort of rapidly progressive in her. And when I think about the things that come into mind immediately as common causes of dyspnea, I think of heart failure or COPD - none of those make sense here.