How many of the patients who have stopped taking medication for 'coronary heart disease' are still alive?
patients who have stopped taking medication for 'coronary heart disease' refer to PATIENT where REASONDESCRIPTION = 'Coronary Heart Disease' and STOP is not null from medications; if deathdate is null, it means this patient is still alive;
SELECT COUNT(DISTINCT T2.patient) FROM medications AS T1 INNER JOIN patients AS T2 ON T1.PATIENT = T2.patient WHERE T1.REASONDESCRIPTION = 'Coronary Heart Disease' AND T1.STOP IS NOT NULL AND T2.deathdate IS NULL