First of all, Kate Chopin's inclusion of the detail of Mrs. Mallard's "heart trouble" represents an important piece of foreshadowing, setting up Mrs. Mallard's abrupt death by heart attack at the story's end. On this point alone, Chopin's decision is an important one, seen through the context of story structure. Authors will usually try to establish key plot devices and plot elements within the text before they directly enter into the story. This same logic is at work here. If Kate Chopin wants Louise's weak heart to prove fatal, she must first establish that Louise had a weak heart to begin with.
That being said, there very well might be symbolic and subtextual levels at play when discussing Mrs. Mallard's heart problems. For one thing, consider how the heart has so often been used throughout literature to represent romantic affections, to such a point as to become synonymous with one another. This entire story, meanwhile, concerns the suffocating nature of traditional matrimony (within the context of the late-nineteenth century), where women are denied true agency by those patriarchal structures and expectations. This image of the weak heart might, then, be read as symbolically linked with Mrs. Mallard's inability to achieve self-fulfillment due to her relationship with her husband.
At the same time, it is unlikely that her weak heart can be read as ironic in and of itself, given that irony relies on the reversal of expectations. That being said, note that the story's ending can be labeled an ironic one: it should be expected, after all, that her husband's safe return should lead to a happy reunion (at least from the mindset of the other characters in the story), not a tragic death. In this sense, Mrs. Mallard's weak heart contributes indirectly to the story's use of irony, as the physical ailment that causes her death, but even so, having a heart ailment means that, at some level, health problems and even heart attacks become a known risk factor, and there should therefore be no surprise that this possibility might turn into reality.