instruction: provide the number of patients whose diagnosis long title is unspecified congenital anomaly of heart and lab test category is blood gas.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE diagnoses.long_title = "Unspecified congenital anomaly of heart" AND lab."CATEGORY" = "Blood Gas"