In our laboratory, we performed 278 transseptal left heart catheterizations in adult patients over a period of 13 years. The left atrium was entered in 91.4% of the intended left heart catheterizations. Of 252 attempts, the left ventricle was entered in 96.1%. Major complications were aortic puncture (0.7%), pericardial puncture/suspected tamponade (3.2%), systemic arterial embolism (1.1%), and suspected perforation of the inferior vena cava (0.4%). There were no deaths. Although less frequently performed during the last decade, the transseptal catheterization technique has a complication rate of the same magnitude as during periods when this method was more commonly applied.