How are they related?

Where did you read that indigestion is a symptom of congestive heart failure? As far as I know, and I just looked in 2 of my med school textbooks, indigestion is not listed as a symptom of congestive heart failure. you can occasionally get loss of appetite and nausea due to fluid buildup, but even those aren't really common symptoms that we look for.

its not a symptom. its just so happens that indigestion causing an acid burn near the thorax region near the heart and heart failure is allso at pretty much the same region hence it is sometimes mistaken heart failure for indigestion.
stress in the heart can cause a build up of acid (feels like indigestion) but an indigestion usually doesnt cause a heart failure.