CDG2009

I was supposed to get a stress test/echo today because I have trouble breathing when I exercise and my heart rate goes up really high. The initial EKG was fine, just showed sinus tachycardia. Then they did an ultrasound(echo) before I was going to start the stress test. They said they couldn't see the walls of my heart very well and that it was just very fuzzy, so they didn't want to go ahead with the rest of the test because it would most likely be inconclusive and would require additional testing. So since insurance usually only covers one test, not both, they told me to come back later to do a nuclear stress test where they inject radioactive fluid into my blood to see my heart better. I asked the sonographer why they couldn't see it very well and she said some people's hearts are just harder to see. So I was wondering if there's something causing the fuzzy ultrasound that they're not telling me. I'm not exactly crazy about having anything radioactive injected into my body, so I'm wondering if that is really necessary, and I want to know why they had so much trouble with the regular echocardiogram. Would a better sonographer be able to see it better, or is it something wrong with me?