Gastric dilatation-volvulus heads the Great Dane's condition list, and among all breeds the Dane carries the highest risk of it. This is the most important paragraph on this page.
In GDV the stomach fills with gas and then rotates, cutting off its own blood supply and trapping the gas inside. Without surgery it is fatal, usually within hours. The conformation that causes it — a deep, narrow chest — is exactly what a Great Dane has.
The signs are: unproductive retching, a swelling or drum-tight abdomen, obvious restlessness and inability to settle, drooling, and pale gums. Any of these in a Dane is an immediate emergency, not a wait-and-see.
Because the risk is so high, many vets recommend a prophylactic gastropexy — tacking the stomach to the abdominal wall during neutering, so it cannot twist. It does not prevent the stomach distending but it prevents the rotation that kills. For this breed specifically, it is a conversation worth having before the dog is a year old.
The Akita is also deep-chested and carries a real bloat risk, though a lower one. Both households should know the signs and know where the nearest out-of-hours surgery is.