Inclusion Criteria- Age >= 18 yd;
- Level 3 cardiopulmonary exercise testing.
Exclusion Criteria- Proven or suspected disease involving severe aortic regurgitation;
- Implanted with a rate-responsive cardiac pacemaker;
- Pneumothorax or pleural effusion;
- Skin lesion(s) at the place where the electrode is supposed to be applied;
- Allergic to adhesive of ECG electrodes.