It is unlikely to have anything to do with a murmur. It sounds most consistent with anxiety or anxiety attacks. It is worth talking to your doctor about. They will likely order a Holter monitor -- 24 hour heart rate monitor -- to determine what your heart rhythm is when you are having symptoms. If you have a murmur, they may also order an echocardiogram.
Can a coroner tell if someone dies from heart arrhythmia?