Among the various reported forms of mechanical intrathoracic injury associated with cardiac catheterization are endocardial laceration, perforation of the heart, intramyocardial and intrapericardial extravasation of injected fluids, hemopericardium, hemothorax, pneumothorax, catheter amputation, and catheter knotting around chordae tendineae, requiring open heart surgical release (3–5, 7–8). Though we are fortunate in lacking personal experience with the foregoing, it is the purpose of this report to describe an additional type of injury fatal to our patient, which in the light of the knowledge gained is preventable. Case Report Selective right ventricular angiocardiography was performed in a 6-year-old white female with tetralogy of Fallot to determine the feasibility of total operative correction. A left subclavian-pulmonary artery shunt had been surgically constructed at the age of ten months. The patient's subsequent growth and development were normal, the height and weight falling within the 50–70 percentile during the last two years of her life. Minimal cyanosis with exercise was noted. Physical examination revealed a blood pressure of 110/90, pulse of 100, and respiratory rate of 20. In addition to the widely audible continuous bruit of a patent anastomosis, there was heard in the left third intercostal space, a systolic ejection murmur and a single second heart sound. The electrocardiogram showed right ventricular hypertrophy. To demonstrate the anatomy of the right ventricular outflow tract right ventricular selective angiocardiography was done (1). Following premedication with 75 mg. Seconal and 0.4 mg. atropine, anesthesia was induced with rectal Pentothal followed by divinyl ether; later open drop ether was used. Since it was found impossible to advance a chosen #7 Rodriguez catheter beyond the right shoulder, this was exchanged for a spring-guided polyethylene catheter (PE 240) of a type we commonly use for percutaneous arterial and left ventricular catheterization. Manipulation of guide spring and catheter was accomplished under fluoroscopic control. When the right ventricle was entered, the guide was removed and thereafter both right ventricular pressure and the electrocardiogram were continuously monitored. Occasional extrasystoles were encountered during passage of the catheter into the right ventricle and in association with the first of two injections of contrast agent. The resulting series of frontal radiographs demonstrated a typical tetralogy of Fallot, a right-sided aortic arch, a left innominate artery and a functioning left Blalock anastomosis (Fig. 1). Definite damping of the pressure curve was noted between the first and second injections. Since this did not seem to be due to clotting, the catheter was withdrawn until undamped right ventricular pressure pulse waves were again obtained (Fig. 2). The second injection which, like the first, consisted of 20 c.c.