SNRI antidepressants (Effexor, Cymbalta, etc) can worsen heart failure.
Heart failure patients have high circulating levels of norepinephrine to compensate for poor cardiac output. Norepi helps to make the heart pump faster and more forcefully.
However, this sustained response increases demand on an already damaged heart...eventually leading to further deterioration of heart function.
It makes sense that drugs that increase norepinephrine MIGHT lead to worsening heart failure.