The purpose of the WHISH STAR study is to investigate whether or not those who are randomized to exercise intervention have higher rates of atrial fibrillation on review of medical records and, in a subset, on screening with a cardiac ECG patch monitor. We will also study whether those with a known history of AF have any changes in AF hospitalizations due to exercise.

The Silent Atrial Fibrillation Recording study (STAR) study is an ancillary study of the NIH-funded Women's Health Initiative Strong and Healthy (WHISH). The purpose of the Women's Health Initiative Strong and Healthy study (WHISH) is to investigate if light to moderate exercise decreases incident atrial fibrillation (AF) among women over 65 who have no baseline AF. The purpose of the STAR study is to investigate the effect of exercise intervention on incident atrial fibrillation ascertained with diagnostic codes. In a subset of women, subclinical atrial fibrillation will be ascertained with cardiac patch ECG monitoring technology (iRhythm's ZIO® XT Patch). This subgroup of WHISH study participants will undergo an 8 day cardiac patch recording at baseline, six (6) months, and one (1) year.

Inclusion Criteria:

• Subjects already enrolled in the parent WHISH study.
• Subjects who are at high risk of developing atrial fibrillation.

Exclusion Criteria:

• Subjects who have had atrial fibrillation at baseline.

The participants are all older women, since the parent study is a post-menopausal study from the Women's Health Initiative.