Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I am sorry to hear that Ares is having episodes which you believe are seizures.
Seizures are rhythmic, repetitive, muscle movements which the dog is unable to control and often loses consciousness during. Many dogs will repeatedly have chewing motions and/or leg motions and can lose urine and stool control. After the seizures the dog will often seem confused and very tired.
Syncope or fainting episodes can look somewhat like a seizure, as the dog may have some twitching and muscle movements and may open and close their mouths or vocalize, but they tend to be less tense and dog seems to collapse and behave as if they are weak, rather then tense, as they lose consciousness. They may pass urine or stool. They tend to recover fairly quickly, as once they collapse (which is due to low oxygen levels due to poor heart function) and relax, the heart is able to catch up, oxygen returns to the muscles and they are able to get up and move around again.
Twenty seconds is a very short period of time for a seizure. In a dog with diagnosed heart disease that would more likely be a syncopal (fainting) episode.
If your pup's heart function is poor enough to have fainting episodes then his heart disease is not well controlled. He may need more drugs added to help his heart muscle function more efficiently, such as Pimobendan. I recommend that your pup see a veterinary cardiologist to have his heart evaluated and get him started on the proper medical therapy.
Best of luck with your fellow, please let me know if you have any further questions.