The pre-death signs of cardiac hypertrophy in dogs include difficulty breathing, coughing, fatigue and weakness, loss of appetite, etc.

Difficulty breathing: When a dog’s heart is enlarged, the heart cannot pump blood effectively, causing congestion in the lungs, and the dog will have difficulty breathing. If your dog is suddenly short of breath, wheezing, or even unable to lie down, this may be a sign of worsening heart hypertrophy.

Cough: When a dog has an enlarged heart, fluid can easily accumulate in the lungs, causing coughing. If your dog coughs frequently and has a noisy cough, it may be caused by an enlarged heart.

Fatigue and weakness: When a dog's heart is enlarged, various parts of the body will be deprived of oxygen, and the dog will easily feel fatigued and weak. If your dog suddenly becomes lazy and unwilling to move, it may be a sign of worsening heart hypertrophy.

Reduced appetite: When a dog’s heart is enlarged, various parts of the body will be deprived of oxygen, which will affect the dog’s appetite. If your dog suddenly loses appetite, or even experiences symptoms such as vomiting and diarrhea, it may be caused by cardiac hypertrophy.