A catheter electrode built into a polyimide tube and inserted intravenously into the heart, which ensures the drainage of action potentials from inside the heart. The hemispherical end of the electrode contacts the inner wall of the heart.
The other pole, a few millimeters away, is in contact with blood only. The diameter of the electrode is 0.4 or 0.8 mm. To facilitate venous insertion, the end of the catheter can be bent at an angle of about 30 degrees if required by the researcher.