A ventricle is the chamber which receives blood from the atrium and pumps it out, away from the heart.
In 2369, Ibudan murdered his clone by perforating the lower ventricle of the clone's heart with a knife. (DS9: "A Man Alone")
In 2374, Dejaren reached into B'Elanna Torres' chest and grabbed her heart, perforating her fourth ventricle. (VOY: "Revulsion")