Does the left ventricle open or close?

The left ventricle does not "open" or "close" in a traditional sense; rather, it contracts and relaxes during the cardiac cycle. During contraction (systole), it pumps oxygenated blood into the aorta through the aortic valve. When the heart relaxes (diastole), the ventricle fills with blood from the left atrium. The opening and closing refer to the aortic valve and mitral valve, which regulate blood flow in and out of the ventricle.