Yes, heart problems may darken your the dark the circle under your eyes. That's because when you have heart problems, the blood vessels under your eyes dilate and make the circles under your eyes darker.
However, you can't affirm that you have heart problems just because of your dark circles, because dark circle is just one of the symptoms of heart problems. Meanwhile, there are many other causes of dark circle as well, such as, aging, allergy, heredity, thyroid problems, deficiency of iron or other key nutrition, liver or kidney diseases.
Therefore, there are so many possible causes of dark circle that we can simply say you have heart problem just because of your dark circle.