It's hard to pinpoint the symptoms. Some people don't know for a while that they have it and experience shortness of breath, dizziness etc. for a while before going to the doctor.
For my DH, he was sick with a fever for a few days, started antibiotics for this viral infection on a Friday. Saturday he was feeling better. Saturday night we actually had an arguement and while he was talking it out with a friend he felt like his heart was going to pump out of his chest. He relaxed and was fine ... we made up, went to bed and then he woke me up at 2AM saying he had a wierd pain in the center of his back. He said it felt like a muscle but not a back muscle because he couldn't pinpoint it. Then his HR was elevated and his BP was fairly high (we monitor it because he has high BP anyway) and then once his hands and feet got cold and numb we went to the ER. At first they said it was a heart attack because this Troponin levels where elevated. Eventually they said it was Myocarditis and the troponin was released due to the damage in his heart as a result of the infection.
His Stress tests where fine, his EKG's where always fine and his Echo was fine. He had decreased heart function at the time but since then has gotten better and all tests are normal.