I read your question carefully and I understand your concern. Since you seem to have had so many tests I suppose they have excluded blood vessel disease by imaging or coagulation issues by blood tests (although I don t know exactly what those tests are). So the most probable culprit in these cases is often the heart. I understand routine EKG was normal, but often there is episodic arrhythmia which might be missed on a single EKG. For that there are some more prolonged investigations in place, starting with 24 h Holter EKG and followed when that reveals nothing by investigation for a week or an entire month (by implanting a device which continuously follows your rhythm-not available everywhere though depends on where you live). At the end of the day there is a percentage of stroke cases where after all exams have been done the cause can not be found. I hope to have been of help.