<s>[INST] when ever i start walking fast or up hill my heart flutters or seams like it skips a beat funny 10 days ago i walked 5km in 46 min and also had 4 bypasses 12 years ago but no shortness of breath or no pain could this be blockage again i have a holter on now ancious to see what come out on it [/INST] Holter will diagnose the character of your ecg when you are having those missed beat and we can plan treatment likewise.  However it is important to note that these features can be total unrelated to blockages and be an independent phenomenon.  If the holter is negative I strongly suggest you to get a stress test done to know if any ischaemia is present,  as after so many years of cabg,  many venous graft tend to degenerate.  Regards </s>