Coronary chronic total occlusions (CTOs) are atherosclerotic plaques comprised of lipid, fibrous and hard calcific material that originate in the vessel wall and extend into the lumen, restricting luminal cross-section by 100% resulting in complete stoppage of blood flow in the affected artery for at least three months. Due to their structure and calcific composition, CTOs are very difficult to treat with existing percutaneous coronary interventional (PCI) techniques. CTOs frequently have a hard fibro-calcific cap on the proximal side with a softer lipidic composition in the interior and distal side. We constructed a novel catheter system with a fiber coupled Ho:YAG laser (2.1um, Coherent Inc) for cutting and a biocompatible CO2 cooling system delivered through a 200um conduit for intravascular cooling. Laser radiation delivered a maximum average power of 20W corresponding to a pulse energy of 300mJ, pulse duration of 200μs, and a pulse repetition rate of 10Hz. Light emitted from the fiber was directed onto ex vivo suspect-calcified CTO arteries (n=3). Successful CTO crossing was achieved in all ex vivo samples. Histological processing showed greater than 50% reduction in residual thermal damage in crossed CTO regions with CO2 cooling compared to no cooling. The miniature device was also used to cross CTOs in an in vivo rabbit femoral CTO model (n=4) under Xray fluoroscopy guidance and subsequent contrast angiography confirmed restoration of blood flow.