Aortic rupture has been in the discussion groups a lot recently. It's not that it's not in other breeds, but the Friesians have a unique location to where their heart failure takes place.
Here is an article about all breeds and Aortic rupture
The more specific information that applies to the Friesian can be read in this Phryso Article.
There are currently no tests available to determine risk. Please see the article to learn about symptoms and diagnosis. As the name implies it's a very serious and fatal condition.
Update, at Utrecht they have successfully used a small ultrasound scope passed through the esophagus near the heart to view the area of the heart that could potentially have the defect. The beauty of this is that it's non invasive and the horse doesn't have to be asleep!! I am not sure the availability of this technology in the US but calling around to major equine universities or clinics should get you some answers.
Friesians show higher arterial blood pressure compared to warmbloods University of Gent research article courtesy Fenway Foundation.
Also please note that there is a specific way to autopsy a Friesian to determine if they died of Aortic Rupture so please contact Fenway Foundation.
Here is a form that helps with some information from Fenway Foundation, if this link does not work please contact them directly .
They may have special instructions for you based on your horses symptoms so please work with them to help identify the source of the problem.
Credit to Sable Friesian Ranch for this article. If you have had or know of a horse that died of Aortic rupture please share stories and information help other owners. Knowing their lineage will also help, but it is not yet determined that it's genetic. It could be fetal development or post birthing complications. Any information you have could help.
Interesting reading can be found by clicking on the following links:
Study by Sandra Havik
Aortiopulmonary fistula in a 25 year old mare (Utrecht, Veterinary Pathology researchgate.net)