Child Has Frequent Episodes Of Passing Out, Breathing Loss Followed By Seizure, Low BP. Could Leaky Heart Valve Be Causing This?

My son is 9 years old, has had 4 episodes of passing out, stopped breathing and then had a seizure. The first episode was when he was 7, then another that year, one when he was 8 and then the last one was this last April. I ve been to a Neurologist and two Cardiologists to rule out the Brain and Heart. His Neurologist thinks it is his heart, but the last Cardiologist found a leaky heart valve but no activity on a Holtom Heart Monitor (24 hours). He has been getting dizzy and have had stomach aches along with his dizzy spells. He is often pale and his blood pressure low. His Pediatrician is going to run blood tests tomorrow because I called in and asked if there are any other signs we are missing. I need advice on whether a leaky heart valve could cause his episodes of passing out and causing the dizzy spells.