While you’re hanging upside down, your heart rate will slow down, resulting in increased blood pressure after only a couple of minutes. This, in turn, as a feedback loop, will cause the heart to pump the blood through your body using a force greater than it might be used to.
So, yes, if you have hypertension, these elevated levels of stress may be detrimental to your health. This also applies to anyone with a heart condition, congenital, or contracted. On the other hand, some doctors have used inversion as a therapy for patients with high blood pressure.
It is known that inversion causes a general state of relaxation, which in turn causes the heart rate to drop drastically. Of course, it should go without saying that you should always check with your doctor if you should invert or find other, better ways to deal with your health issues.