Abstract
The occurrence of right ventricular infundibular spasm during right heart catheterization has been recorded and is now reported. This is thought to confirm the suggestion that cyanotic attacks in Fallot''s tetralogy are due to such spasm. The hypothesis that this is precipitated by increase of circulating norepinephrine is put forward and evidence is presented in support of this. Prevention and treatment of the cyanotic attack are discussed in the light of this hypothesis.