Anti-Estrogens

Hey guys i have a problem. I was running some t-prop and i started taking some arimidex at like .25mg EOD. Well after like my 3rd dose of it my heart started racing and i had a crazy irregular heartbeat for like 3 days eventually i had to go to the ER. Thank god everything turned out ok. My question is if i cant use these any other good ideas on what i should do?