After Londo Mollari's shirt is pulled open in MedLab, the shirt is pulled closed twice.
When discussing Mollari's heart condition, Dr. Franklin says "bi-pulmonary", meaning the centauri have two hearts. But "pulmonary" refers to lungs, not heart. The term should be "bi-cardiac".
A defibrillator is used to restart Londo's arrested heart. As the name suggests, a defibrillator is used to stop a heart that is undergoing atrial fibrillation (when the heart's muscle cells are no longer working together to produce a pumping action). It cannot restart a heart in cardiac arrest (this is a common error in TV shows and movies).
Londo says he has never apologized for anything in his life; this is not true. He apologized (sincerely) to Mr. Garibaldi in Babylon 5: The Gathering (1993) and apologized (under duress) to the technomage Elric in Season 2's The Geometry of Shadows (1994).
In the scene when Vir appears in Londo's dream, a boom mic is clear on the right side (then to the top, as the camera rotates) of the screen.