My Husband Is 55 Yo With Type 2 Diabetes, And

My husband is 55 yo with type 2 diabetes, and is on meds for heart issues. His cardiologist is preparing to run tests on him to find out what's wrong. His doctor recently put him on Isosorbide mononitrate, for the spells he has had just recently (pains and pressure spells) and with isosorbide comes headaches, quite severe headaches. Jeff's BP is running 156/92 w/ a heart rate of 66.
At what point do I need to take him to the ER? Thank you!
Dee