Adaptive Cardiac Resynchronization Therapy Optimization at Rest and During Exercise (AdOPT CRT)

Inclusion Criteria: * Subject is age 18 or greater * Subject is willing to sign and date the study Informed Consent form * Subject has been implanted with a clinically indicated CRT-D device (Medtronic Vision 3D or Protecta models) for at least 1 month but less than 7 months from the date of study enrollment Exclusion Criteria: * Subject has a history of persistent or permanent AF for which pharmacological therapy and/or cardioversion have been unsuccessful or have not been attempted. * Subject has atrial or ventricular tachyarrhythmias or frequent atrial or ventricular ectopy at the time of enrollment. * Subject's resting heart rate at the time of enrollment exceeds 90 bpm. * Subject had CRT system implanted for more than 7 months from the date of the study enrollment * Subject has complete AV block. * Subject had previous mechanical valve surgeries. * Subject has congenital heart disease. * Subject has contraindication for an exercise test. * Subject is unable to perform a sub-maximal exercise test. * It is not possible to acquire technically acceptable echocardiographic images. * Subject has medical conditions that would limit study participation. * Subject is pregnant (all women of child-bearing potential must undergo a pregnancy test within seven days prior to the study visit). * Subject is enrolled in the Adaptive CRT study * Subject is enrolled in concurrent studies which could confound the results of this study. * Subject meets exclusion criteria required by local law