I spent six months as a massage therapist intern (basically massaging people one day per week for free) and one year as a licensed massage therapist after that. The most common request I received was to work on people's traps (the middle head, specifically). When I say this was the most common request, I mean about two of every three people had self-described tension/pain/tightness/stiffness in this area (the usual cause of this is that these muscles are chronically contracted due to normal stress reaction or to maintain oneself in a desk-working position).
Those people typically left very happy and tension-free from the massage tables of myself and my peers, but the effects didn't last long. Our clients would return to their usual lifestyles and habits...and to their usual trapezius issues. Fortunately, over the past few years in my practice as a personal trainer, I have come up with a longer lasting, more effective solution: perform a set of shrugs.
One of my newer clients, Jon, has been experiencing trapezius "tension" for a while. He works 40+ hours per week at a desk job and has been exercising for years. A few weeks ago, I put shrugs in his regular routine (1-2x per week). On Tuesday, Jon came in and told me that he hasn't felt anything in his traps since we started the shrugs. While Jon is certainly not the first, he is the most recent success of this method.
Why does this work? There are two reasons, I believe: if your muscle fibers are fatigued, they can't be tense (contracted). Also, performing a challenging set of shrugs will increase the blood flow to the area for several days.
If you want to try this out and don't have a shrug machine, dumbbells or a cable machine will work just as well. Pick a resistance that's moderately challenging at the start and work till muscle failure, just like any other exercise. Your shoulders should move straight up and down.
In my observations, a challenging set of shrugs has been more effective than direct massage in eliminating trapezius tension. I can't guarantee you that shrugs will work, but it's been highly successful with my clients. I'm not discouraging you from going to a massage therapist. If you have this problem and still plan to see a massage therapist, ask to have your chest worked on (for those female readers, this is non-invasive). Massage strokes that work on the pectoralis major, an opposing muscle group, can reduce the trapezius tension just as well as direct massage.