Your husband should check with his doctor. If there is severe cardiovascular disease, it is advised not use the inversion table.
It seems when your body is an upside-down position for more than a few minutes, the heart rate slows as the blood pressure rises. As a result one should not use an inversion table if the individual suffers from cardiovascular disease.
An enlarged heart can indicate a serious heart disorder, and that would be the issue the doctor would have to make to approve the exercise.
Hope this helps, and if you have any followup questions, you are welcome to respond. Thanks for the question, take care.