Abstract: A cryogenic medical device for delivery of subcooled liquid cryogen to various configurations of cryoprobes is designed for the treatment of damaged, diseased, cancerous or other unwanted tissues, particularly as utilized for the ablation of cardiac tissue in the treatment of atrial fibrillation. The device is a closed or semi-closed system in which the liquid cryogen is nitrogen contained in both the supply and return stages. The device is capable of generating cryogen to a supercritical state, specifically supercritical nitrogen, and may be utilized in any rapid cooling systems. As designed, the device also integrates endocardial catheters and epicardial probes.