With the introduction of interventional procedures such as percutaneous mitral valvuloplasty and radiofrequency ablation of left-sided bypass tracts, there has been renewed interest in the technique of transseptal left heart catheterization. We review our experience with 1,279 transseptal catheterizations performed over the last 10 years. The most common indications for transseptal catheterization included direct measurement of left atrial pressure or access to the left ventricle in patients with prosthetic aortic or mitral valves, and in patients undergoing percutaneous mitral valvuloplasty. A total of 17 major complications occurred (1.3%), including cardiac tamponade (15 patients, 1.2%), systemic emboli (1 patient, 0.08%), and death secondary to aortic perforation (0.08%). We conclude that when performed by experienced operators, transseptal left heart catheterization is associated with low morbidity and mortality.