Wagtail
Horse servant
I know of someone who lost a horse that they had purchased as a fit and ready to go eventer who she had vetted and passed with flying colours. Three weeks later she had a heart attack while jumping into the water on their first xc together. This was not picked up in the vet report.
Vettings do not pick up everything, no. A heart condition can develop at any time. However, I would rather be aware of anything that a vetting might highlight if I wanted to put my horse into hard work. To me, it is just a sensible thing to do. It's not hard or ridiculously expensive. Just one five star vetting (no more expensive than a good rug, and a one off), and then vet does quick check over at vaccination time. It took the vet ten seconds to detect the heart problem of the mare I mentioned above.