A 14-year-old castrated male Shih Tzu presented with acute hemorrhagic vomiting. The initial medical records indicated a probable diagnosis of acute gastritis due to inappropriate food intake. Although gastrointestinal (GI) endoscopy was the preferred diagnostic approach, the client declined anesthesia because of the dog’s underlying heart condition. Therefore, we opted for anesthesia-free capsule endoscopy. The procedure identified severe gastritis with no detectable abnormalities in the other GI regions. Following diagnosis, dietary modifications and omeprazole treatment were initiated, resulting in the resolution of clinical symptoms. Follow- up capsule endoscopy 3 weeks later verified a significant improvement in gastritis. This case highlights the potential of capsule endoscopy as a valuable diagnostic tool in patients presenting with acute vomiting.