My husband collapsed on the train a couple of weeks ago an has since has a 24 hour heart moniter, an ecg and a brain MRI. the heart and brain were clear, except that his notes say he has a sinus arrhythmia. he is 27 and otherwise healthy, realatively fit, a former athlete, and aside from the occasional cold or flu, has no previous medical issues. Basically, his gp could not explain what is wrong and wont clear him to return to work and wants him to see a cardiologist. what we want to know is what is a sinus arrhythmia? is it serious? should we be worried? is keeping him off work going to be a long term thing if he does have a sinus arrhythmia?