<s>[INST] I was recently diagnosed with dilated cardiomyopathy.  My EF is 35%.  I take 3.125 mg of Coreg twice per day.  Today, while sitting watching a video, my heart rate, which is usually in the 72 - 78 beats per minute range was up around 90 beats per minute.  I also had a single shooting pain down my left arm and a general feeling of numbness in the arm after that.  I had this happen once before and the shooting pain in my left arm was so strong it woke me out of a sound sleep.  Do you have any idea what might be causing the shooting pain and racing heart rate?  Is this something I should be going to the ER for?Thanks,Scott [/INST] The pain in cardiomyopathy could be due to coronary artery disease / angina. You should go in for more tests to know the exact cause and have treatment accordingly. Yes it could be serious. </s>