How many patients of Irish ethnicity take medication for 'myocardial infarction'?
take medication for myocardial infarction refers to medications.REASONDESCRIPTION = 'Myocardial Infarction';
SELECT COUNT(DISTINCT T1.patient) FROM patients AS T1 INNER JOIN medications AS T2 ON T1.patient = T2.PATIENT WHERE T2.REASONDESCRIPTION = 'Myocardial Infarction' AND T1.ethnicity = 'irish'