About one-third of patients with stroke have no documented cause for the cerebrovascular event (known as cryptogenic strokes). Atrial fibrillation is a common cause of stroke, but when transient (paroxysmal) it may remain undiagnosed. Recent data suggest that occult paroxysmal atrial fibrillation may be identified in patients with cryptogenic strokes using prolonged ambulatory cardiac rhythm monitors.

The investigators designed this study pursuing the following goals:

1. To determine the prevalence of occult paroxysmal atrial fibrillation in patients with cryptogenic stroke using long-term mobile cardiac outpatient telemetry.
2. To compare this prevalence to that found in a control group with stroke of known, non-cardioembolic cause.
3. To look for clinical, laboratory, echocardiographic, and imaging data that serve as risk factors for occult paroxysmal atrial fibrillation in patients with cryptogenic stroke.
4. To examine the utility of mobile cardiac outpatient telemetry, a relatively new diagnostic tool, in the evaluation of patients with cryptogenic stroke.

Inclusion Criteria:

• Stroke or TIA within previous 3 months
• Stroke work up including: EKG, serum lipids, serum TSH, TTE or TEE, brain CT and/or MRI, Vascular Evaluation of head and neck using any combination of ultrasound, MRA, CTA, and conventional angiography

Exclusion Criteria:

• Documented history of atrial fibrillation or flutter
• PFO closure planned before conclusion of the monitoring period
• Incomplete stroke work up

Patients with stroke or TIA confirmed by a vascular neurologist within previous 3 months with complete evaluation for stroke causes according to current standards.