Hypertrophic cardiomyopathy with congestive heart failure. Sinus tachycardia.
Simultaneous viewing of the ECG and heart sounds confirms that the tachycardia is sinus in origin. Heart rates in excess of 180 bpm and up to 240 bpm are not unusual for stressed cats in a veterinarian's office.
A gallop in a cat is typically a S4 gallop, however the heart rate is too fast in this case to distinguish S3 from S4.
For more on gallops visit the following page.