Hello and welcome to Healthcare Magic. Thanks for your query.
Palpitations are very common with 
anxiety disorders. It is important to understand that anxiety can present with not only psychological symptoms but also with physical or bodily symptoms. 
Rapid heart rate (palpitations), 
chest tightness or discomfort, etc. can are all commonly seen in people with anxiety.
You can practice relaxalation techniques like deep breathing, yoga, 
meditation, etc. to overcome your anxiety symptoms.
You have also mentioned that you also have 
Mitral Valve Prolapse, which could be another possible cause for your palpitations. But this is also not a serious problem. If you have already had a cardiac elaluation and were told that there are no complications associated with the Mitral Valve Prolapse, then you needn't worry about this also.
Wish you all the best.
Regards,
Dr. Jonas Sundarakumar MBBS., DPM., MRCPsych.(U.K.)
Consultant Psychiatrist