The objective of this study is to assess the accuracy of the Apple Watch 4 Series watch in generating an ECG that is suitable for determination of heart rhythm compared to rhythms monitored via telemetry. Secondary objective is to assess the accuracy of the Apple Watch 4 series watch in identifying atrial fibrillation when it is present.

The study will assess the accuracy of the Apple watch 4 series watch when worn by post-operative cardiac surgery patients after they have transferred from the ICU to the cardiac telemetry unit.

During testing each subject will wear:

1. An Apple Watch 4 series watch for no more than 5 minutes.
2. Standard continuous telemetry monitor

The location of the watch (left or right wrist) will be randomly assigned.

Heart rate and rhythm will be assessed by obtaining tracings from the Apple Watch 4 series watch while at the same point in time obtaining tracings from a standard telemetry monitor.

ECGs from the Apple Watch 4 will be collected by asking the patient to place his/ her finger on the digital crown of the Apple Watch 4 for 30 seconds. The rhythm displayed by the Apple Watch 4 will be viewed on the Apple health app (available on the iPhone 8) and will be saved for subsequent viewing and analysis.

Each enrolled patient will have a minimum of three assessments of heart rhythm per day for at least two days, generating a minimum of six data points per patient.

After conclusion of the study for each subject, the ECG's from the health app pertaining to that subject will be reviewed by a board certified cardiologist as will the telemetry tracings.

In order to obtain tracings of new onset post-operative atrial fibrillation. 50% of the subjects enrolled will be in sinus rhythm and 50% will be in atrial fibrillation at the time of enrollment.

Inclusion Criteria:

• Age > 18 years
• Post-operative cardiac surgery patients on the cardiac telemetry floors at the Cleveland Clinic Main Campus

Exclusion Criteria:

• Presence of a cardiac pacemaker
• Use of a radial artery graft for coronary artery bypass grafting
• Tattoos located on the skin of the wrist or forearm where the Apple Watch 4 will be placed