Spinnaker Formation of Sinus Venosus Valve

A persistent right valve of the sinus venosus fatally complicated a case of tricuspid atresia in a 10-year-old boy. The center of this large membrane stretched to form a sac resembling a spinnaker. Depending on the relative amounts and directions of blood flowing against it from the coronary sinus below and the venae cavae above, the sail might fill or empty quickly. This gave means of potential obstruction: either of coronary venous flow which, without a tricuspid valvular orifice, could be trapped beneath the membrane; or of all right atrial flow if the sac fell across the sole atrial outlet, the septal defect. Such episodic block caused syncope six times in the last 23 months of life and death in acute right heart failure.