Abrupt changes to one's lifestyle disrupt biorhythms. Acute effects are well known from jet lag where transmeridian travel leads to insomnia, fatigue, irritability, gastrointestinal symptoms and other complaints. Several studies in the hospital environment reported dampened and misaligned biorhythms, suggesting that the inpatient experience is replete with circadian disruptors. However, comprehensive assessments of how circadian clocks are affected in intensive care and how this predicts post-operative recovery and risk are largely missing.

Inclusion Criteria:

• Adults scheduled for cardiac surgery;
• ≥18 years of age;
• Capable of giving informed consent;
• Own a smartphone (Apple devices only).

Exclusion Criteria:

• Taking sleep aids (antihistamines, melatonin, etc.)
• History of alcohol abuse (more than 2 drinks a day with last drink within the past 3 days)
• History of substance abuse at risk of postoperative withdrawal;
• Active diagnosis of alcohol or substance abuse;
• Recent travel across more than two (2) time zones (within the past month);
• Planned travel across more than two (2) time zones during the planned study activities;
• Subjects, who have received an experimental drug, used an experimental medical device within 30 days prior to screening, or who gave a blood donation of ≥ one pint within 8 weeks prior to screening;
• Subjects without access to WiFi in their or close to home or at work;
• Patients with hearing aids;
• Heart transplant patients;
• Patients in isolation.

Potential patients will be screened from outpatient clinic schedules from cardiac surgery appointments within the Perelman Center for Advanced Medicine. Patients for whom cardiac surgery is advised and who meet eligibility criteria will be approached and enrolled after their consultation with the surgeon.