Introduction: Using conventional transseptal needle puncture and guided by x-ray fluoroscopy (XRF), the consequences of errant punctures through the free wall of the atria or into the aorta are well known to experienced operators. The incidence is even higher in patients with abnormal atrial septal morphology.Puncture using a small laser catheter instead of a needle has thetheoretical advantage of a blunt instrument that perforates tissue onlyduring controlled activation, and that may require less force than aneedle. Also, the use of modern innovative imaging technique as realtime MRI (rtMRI) and XFM (X-ray Fused with MRI) may enhance thesafety of transseptal puncture, facilitate procedure, and increase operator confidence. In the current study, we evaluate the feasibility and safety of laser transseptal puncture in a swine model, and guided by 3 different imaging techniques.Methods: A total of Twenty five swine underwent laser transseptalpuncture guided by XRF (n=8), rtMRI (n=7), and XFM (n=10).We used a commercial excimer laser catheter (0.9mm Clirpath,Spectranetics), and customized a number of them with a receiver coil to impart MRI visibility at 1.5T. The laser catheters were steered using avariety of delivery catheters to target fossa ovalis. After traversing theseptum into left atrium, procedural success was corroborated bypressure, oximetry, angiography, and necropsy. Intentional non-targetperforation simulated serious complication.Results: The 0.9mm laser catheter traversed in vitro targets with reduced force compared with a Brockenbrough needle. For rtMRI procedure, embedded MRI-antennae accurately reflected the position of the laser catheter tip and profile in vitro and in vivo. Despite increased profile from the microcoil, the 0.9mm laser catheter traversed in vitro targets with similar force (0.22 ± 0.03N) compared with the unmodified laser.Laser puncture of the atrial septum was successful and accurate in allanimals, evidenced by oximetry, pressure, angiography, and necropsy.The laser catheter was steered effectively using a modified Mullinsintroducer sheath and using two different deflectable guiding catheters.The mean procedure time was 15 ± 6 minutes for XRF, 31 ± 9 minutes forreal-time MRI, and 13±4 minutes for XFM), with an range of 2-4 secondsof laser activation. There were no adverse sequelae after prolongedobservation. Necropsy revealed discrete 0.9mm holes in all septae.Under rtMRI, Intentional perforation of the aorta and of the atrial free wall was evident immediately. Conclusions: Laser puncture of the interatrial septum is feasible andsafe, using a blunt laser catheter that perforates tissues in a controlledfashion. Instantaneous soft-tissue imaging utilizing rtMRI providesimmediate safety feedback. Real-time MRI and XFM are promisingtechnologies that may -With further development - improve the safety and success rate of a range of complex endovascular interventions, and may bring complex interventional procedures to a broader base of physicians by making them simpler to perform.