Pulmonary vein isolation (PVI) is an established rhythm-control therapy for atrial fibrillation (AF), yet the electrophysiological response of post-PVI individuals exposed to hyperbaric environments remains undocumented. Similarly, the in-vivo performance of implantable loop recorders (ILRs) and external patch-based electrocardiographic (ECG) devices under increased ambient pressure has never been reported. We describe the first hyperbaric electrophysiology assessment in a post-PVI diver undergoing both underwater immersion and dry hyperbaric exposure with dual-modality cardiac rhythm monitoring. A 46-year-old experienced diver with successful PVI underwent: a scuba dive to 42 m in a warm water pool, monitored with a marinised 12-lead ECG Holter system; and a stepwise hyperbaric chamber compression to 284 kPa (2.8 atmospheres absolute) in ambient air, with single-lead surface ECG recordings obtained at static pressure plateaus. In both cases, the subject was monitored as well by his ILR. No AF recurrence or other dysrhythmias were detected during either exposure, with stable heart rate trends. The ILR maintained full functional integrity after both the 42 m dive and the 284 kPa chamber compression. The external ECG patch yielded interpretable tracings during static phases. Telemetry failed due to electromagnetic shielding by the steel chamber walls. This case suggests that carefully selected post-PVI individuals may tolerate controlled underwater and hyperbaric exposure without rhythm destabilisation. Both implantable and external monitoring devices preserved operational integrity under moderate hyperbaric conditions, providing a foundation for the emerging field of hyperbaric electrophysiology monitoring and informing fitness-to-dive assessment in post-ablation patients.