Last Summer I Had A Heart Cath Done. Dr Said

Last summer I had a heart cath done. dr said I had 50% blockage in a vein. He put me on Metoprolol 50 mg. Now I am having fluttering in my heart followed by cough...I have appt next Tues..I am concerned about heart attack or stroke..What causes this fluttering, I am diabetic-metformin 500 mg 2x' day, low thyroid - synthroid .75 Thank you for your help.