AI analysis of ECG recordings from 96,531 UK Biobank participants identified 2,399 individuals with asymptomatic atrial fibrillation who had no prior clinical diagnosis. Over nearly 5 years of follow-up, these participants showed a tripled ischemic stroke incidence (1.5% versus 0.52% in those without AF) and 62% higher risk of major cardiovascular events including heart attack and cardiovascular death. This represents a critical middle ground between undiagnosed individuals and those with clinically recognized atrial fibrillation, who had even higher stroke rates at 3.4%. The findings suggest millions of adults may harbor undetected heart rhythm abnormalities that substantially elevate their cardiovascular risk. This could revolutionize preventive cardiology by enabling earlier identification and anticoagulation therapy to prevent strokes. However, the clinical utility remains uncertain given potential false positives and unclear treatment thresholds for asymptomatic cases. The economic and psychological implications of widespread AI screening also warrant consideration. As this is a preprint awaiting peer review, these promising but preliminary results require validation before clinical implementation.