The feasibility of a novel catheter system of percutaneous transluminal cardiomyotomy and valvulotomy was examined in anesthetized dogs. The system was composed of a guiding balloon catheter, a cardioscope, and a pair of scissors with or without guide wire at the distal tip. The system without guide wire was introduced into the left ventricle, the balloon was inflated and was pushed against the endocardial surface. After confirmation by cardioscopy, the targeted tissues were incised by the scissors. By these maneuvers, the trabeculae, papillary muscles, and chordae were incised or transected in 7, 6, and 6 of 7 dogs, respectively. The system without guide wire was advanced to the aortic root, the guide wire was introduced into the left ventricle to prevent dislocation of the catheter system, the balloon was manipulated against the aortic cusp and the cusp was successfully incised with cardioscopic guidance in all five dogs. The results indicate that percutaneous transluminal cardiomyotomy and valvulotomy can be performed with cardioscopic guidance.