1366 infants in the first year of life had cardiac catheterisation with or without angiocardiography in our Department of Cardiology between 1963 and 1973. The overally mortality in the first 24 hrs after the cardiac catheterisation for the first year of life was 1.83%. The subdivision of the first month of life reveals the high mortality rate of the first two weeks of life with the highest percentage of 18.9% in the first week of life and with 10.7% in the second week of life. After that time the mortality is significantly decreasing, but still amounts to 7.6% in the first month of life. There had been no death after the seventh month of life. 14 of the 24 infants died without a specific event in increasing heartfailure and/or acidosis. In the other 10 cases death was due either to the manipulation of the catheter (partial-perforation or perforation), to the angiocardiogram (subsequent asystole) or to the position of the catheter with subsequent intramural injection of contrast material.The best correlation was between the mortality and the severity of the underlying cardiac malformation. Further complications which did lead to death 24 hrs following cardiac catheterisation are described. Our results are compared with those of other authors. The reasons of various complications are discussed. Cardiac catheterisation and angiocardiography as early as possible is necessary because palliative procedures and corrective surgery can be initiated immediately. But it is important in the very sick infant to shorten the procedure as much as possible and to keep angiographic injections at a minimum.