Hypercyanotic attacks occur as a result of an increase in systemic dilatation and spasm of the infundibulum thereby rapidly increasing right ventricular outflow obstruction. The spasm may be caused by sympathetic stimulation.
Other causes include anything which increases systemic vasodilation, thus:
Annotations allow you to add information to this page that would be handy to have on hand during a consultation. E.g. a website or number. This information will always show when you visit this page.