Hello and thank you for using HCM. I carefully read your question and I will try to explain you something and give you my opinion. When we deal with a syncope we have to evaluate cardiac and neurological problems. According to cardiac issues. There are different cardiac reasons that might cause a syncope. The most important one are rhythm issues like atrio-ventricular block, severe bradicardia, long heart pauses, arrhythmia. All sow it is quite known in cardiology that sometimes several people do heart blocks after cardiac surgeries. To exclude cardiac factors it is mandatory to do some examinations. It is very important to verify in what situations does the syncope happen each time, in what situations. So, if I was your treating doctor i will recommend cardiac echo-cardiography and the most important a holter rhythm monitoring for minimally 48 h. This rises the possibility to catch any problem. You must know that the rhythm monitoring is random, it might happen that you do it but it doesn t happens anything with your rhythm during that day and so we don t catch anything, So it is mandatory to take it as long as possible and repeat it. According to the Carotid result, it doesn t explain the syncope. So my opinion is to continue and do holter rhythm monitoring and if no result, maybe a head CT scan. Hope I was helpful. Wish your father good health. Best regards.