Inclusion Criteria:  Age 18 years or older undergoing cardiothoracic surgery that is male or a non-pregnant female and are amenable to using one of the wearable devices of interest (Fitbit and iWatch). Individuals willing to provide informed consent and who have capacity for all study procedures  Exclusion Criteria:  Individuals with mental incapacity and/or cognitive impairment that would preclude adequate understanding of, or cooperation with the study protocol. Any pregnant participant. Severe irreversible pulmonary hypertension. Congenital heart disease Chronic renal insufficiency or undergoing chronic renal replacement therapy Liver cirrhosis