I get frequent tightness and pain in my arms. It's mostly spasticity, but I have some pain from hand soreness (playing the upright bass) or working with leather. So I try to stretch out my arms and hands, and massage them as much as possible.
What helps me most is regular doses of baclofen and zanaflex. I take 60 mg a day of baclofen, and zanaflex when needed.
Nitro helps heart pain because it dilates the coronary arteries (and all blood vessels so lowers BP and causes severe headache) so more blood can carry more oxygen to the heart and stop the pain of starving heart muscle.
The heart is made of a different kind of muscle tissue. It isn't supposed to complain about regular 'spasms'. Heaven forbid muscle relaxers and antispasmotics worked on the heart like they do on skeletal muscle.
When I had the type of spasms and pain you describe bloodwork showed an acute inflammatory process was going on (sky high sed rate, aka ESR). I was started on oral Prednisone that tapered over two weeks (and then had to be repeated for better symptom resolution). The dose was more than twice what's in a Medrol dose pack but not anywhere close to what is used for a MS exacerbation.
In the mean time gabapentin was gradually added to the baclofen I had been taking already. In the end, the baclofen could be reduced a little and I found a combination of the two drugs that controls both spasticity and pain reasonably well.
Apparently I have a second inflammatory autoimmune disease (or two or three) making their presence known in weird ways. I don't know if this will be helpful but it might be worth a try. Sometimes it seems harder than it should to find a winning combination. I had to press for an answer because narcotics offered NO relief. They just made me more likely to fall while in pain.
Hope you've found help by now.
Mary