WHOOP ECG Software Performance Assessment Study

Inclusion Criteria: * Aged 22 years or older. * Ability to provide informed consent. * Willing to participate and to follow the procedures per the Principal Investigator's instructions. * Resided in the United States. * Wrist circumference: 130 mm to 245 mm at band wear position. * Previous medical history of persistent, paroxysmal, or permanent or chronic AF and being in AF at time of enrollment (AF cohort only). * No known history of AF and being in normal sinus rhythm at the time of enrollment (NSR cohort only). Exclusion Criteria: -Subjects with an implantable pacemaker device or implantable cardioverter- defibrillator device. * Medical history of a life-threatening cardiac arrhythmia, e.g., ventricular tachycardia or fibrillation. * Any known allergies to medical adhesives, isopropyl alcohol, or ECG patch. * Any known allergy or sensitivity to thermoplastics, metals with physical vapor deposition (PVD) coatings or Elastane used in the wrist fitness devices. * Clinically significant body tremors that compromise study measurements. * Pregnant at the time of enrollment. * Any physical disability that prevents safe and adequate testing. * Physical or medical impairments that preclude exercise testing, including, but not limited to, back pain and leg claudication. * Mental impairment as determined by the Investigator, or designee. * Subjects with any medical history, physical examination finding, vital sign or other finding or assessment that could compromise subject safety, study integrity or accurate assessment of study objectives. This includes, but is not limited to, known untreated medical conditions that may be considered clinically significant, such as significant anemia, electrolyte imbalance, untreated or uncontrolled thyroid disease, and open wound(s) in the area of test band positioning. * Vital sign measurements, medical history or physical examination finding that makes the subject inappropriate for participation according to the Investigator. * Scarring, tattoos, large, pigmented moles, or other skin pathology in the area of sensor location. * Severe skin conditions on either wrist, that would preclude wearing the sensor. Severe symptomatic skin injury, disorder, allergy, or disease such as eczema, rosacea, impetigo, dermatomyositis or contact dermatitis on wrist or other areas where sensors or electrodes would be placed. * Clinically significant hand tremors as judged by the Investigator. * Participated in phase 1 of the study (Only for phase 2 cohort).