Match the structure to its description. Description Structure A cluster of cells located in the interatrial septum that delays the electrical signal before it passes to the ventricles. dropdown The pacemaker of the heart, located in the right atrium, responsible for initiating the heartbeat. dropdown The valve located between the right atrium and right ventricle. dropdown The layer of the pericardium that covers the heart directly, also known as the epicardium. dropdown Blood vessels carrying oxygenated blood from the lungs to the left atrium. dropdown