You are probably referring to the septum wall. That is the wall that separates the left and right lower heart chambers, and the thickness has an estimated range of 6 to 11 mm.
Thickened heart walls reduces the filling capacity, and usually the rigidity impairs to some degree the ability to pump as well. If this condition is serious, it can cause shortness of breath, etc. but an overweight and poor physical condition can also cause the problem, and the back problems may be preventing a good exercise routine. If you have access to swimming, that would help you get into a better physical condition.
You can live out a normal life span with good care, medication that reduces the heart's workload, proper diet, exercise, etc. .