[Verse 1] Four rooms share one wall between them, a septum built with different mortar— some patches thin as paper, some thick as bone, and where it fails writes the whole report. Cardiologists drew a map with quadrants, outlet, membrane, inlet, muscle floor, learn the zip code of the leaking and the anatomy tells you more. [Chorus] One's the Outlet, riding under the valves, subarterial, supracristal, doubly committed—same address. Two's Perimembranous, the busy corner, seventy to eighty percent, it's nobody's guest. Three's the Inlet, AV canal neighbor, five to eight, low by the tricuspid crest. Four's Muscular, trabecular scatter, fifteen to twenty, Swiss cheese at its best. [Verse 2] Outlet's the rare one here in the West, barely five percent, quiet and small, but cross the Pacific, the numbers triple— thirty in Asia, don't ignore the call. Synonyms stack like aliases on a passport: conal, infundibular, juxta-arterial too, doubly committed 'cause both great vessels sit right above it, nothing in view. [Verse 3] Now the busy one, Perimembranous, membranous, paramembranous, conoventricular name, seventy to eighty percent of all comers, the membranous septum takes the blame. It can stretch its arms toward the inlet, lean toward outlet, wear an extension coat— one location, many costumes, still the same hole, still the same boat. [Verse 4] Inlet sits where the AV valves are tethered, canal-type cousin to the cushion defect crew, five to eight percent, low and posterior, mind the conduction tissue passing through. Muscular's the trabecular wanderer, single or scattered, a modest share, some close themselves before you've finished charting— holes that vanish like they were never there. [Bridge] Careful now, don't cross the wires: Type Two here is Perimembranous, plain— but Collett-Edwards numbers truncus different, their Type Two shares nothing but the name. A truncus baby's hole sits subarterial, outlet family, Type One on our chart— never call it Type Two out of habit, two systems, don't let them mix up the heart. [Chorus] One's the Outlet, riding under the valves, subarterial, supracristal, doubly committed—same address. Two's Perimembranous, the busy corner, seventy to eighty percent, it's nobody's guest. Three's the Inlet, AV canal neighbor, five to eight, low by the tricuspid crest. Four's Muscular, trabecular scatter, fifteen to twenty, Swiss cheese at its best. [Outro] Outlet, Perimembranous, Inlet, Muscular— four locations, one wall to explore. Say the number, know the neighborhood, that's the scheme that the clinics adore.
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