The original seems to read 'Ovarian disease, syncope' and the RCE says 'Syncope ..... disease of the heart' but I am not sure what the ..... is.
There's nothing specific to say that Dr Littlejohn knew what was wrong with her before she died, but it's not unlikely that he did, if he was her regular doctor.
According to my ordinary dictionary, syncope is 'a fainting fit from sudden anaemia of the brain'. I believe that it is associated with irregularity of the rhythm of the heart, which would fit with the reference to 'disease of the heart' in the RCE.