instruction: what is the number of patients whose year of birth is less than 2109 and diagnoses short title is mitral/aortic val insuff?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.dob_year < "2109" AND diagnoses.short_title = "Mitral/aortic val insuff"