The patient is 45 years old. She complained of interruptions in the heart, dizziness, weakness, a sense of cardiac arrest. On the ECG, the rhythm is correct, sinus, heart rate of 75 per minute. In standard leads, after one normal contraction, an extraordinary, premature contraction of the heart with a deformed ventricular complex is recorded, there is no P wave in front of it, a full compensatory pause. Questions: 1. Indicate disturbance of excitability on an ECG? 2. The mechanism of occurrence of this violation? 3. According to the number of foci, a violation of excitability may be