RESPERATE BREATHING TRIAL In subjects who have MCD, to know whether a controlled breathing relaxation technique using an FDA-approved paced breathing device, RESPeRATE, helps with chest pain and shortness of breath and to test to see if this form of biofeedback or relaxation technique helps with heart rate variability during mental stress, MCD subjects will be randomized to completing a RESPeRATE breathing trial or performing their own choice of relaxation technique for 8 weeks.