A cat’s heartbeat is very fast and its belly is shaking all the time. This may be a stress reaction caused by nervousness, fear, and anxiety. It may also be respiratory disease, lung disease, ascites, or pleural effusion. You need to observe the cat’s status. If the cat is just suffering from Don’t worry if this happens when external stimulation occurs, just calm the cat’s mood; if the cat has this situation frequently and has difficulty breathing, it is best to send it to a pet hospital for examination and treatment.