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.
Yes, some heart problems may lead to dark circles under eyes because of the bad blood circulation. The dark circles under eyes could also be caused by the stay up late at night. Since you have the dark circles, you may have some problems at the body. It maybe cause the heart problems that you need to take notice of. You should have the good rest and good diet every day to keep the health of the body and the eyes.
Don't worry too much about it. The heart problems can lead to dark circles, but it doesn't mean that you get heart problems. Because there have so many reasons that will cause this symptom, not only the heart problems. For example, if you have kidney problems, at long ill body empty, overworking and sleep deprived. So, recently take regular breaks and vocations. If you are not at ease, you can go to the hospital to check your body.