Heart lies obliquely in the mediastinum (base to right, apex to left) Delays ap between atria and atrioventricular bundle called av node. Conduction of cardiac activity in cells by intercalated discs and gap junctions. 1/9/2017 3:09:00 am: heart rests on diaphragm, heart lies in mediastinum (sternum to vertebral column, from first rib to diaphragm and between lungs, most of mass of heart lies to left of body"s midline (2/3) Clinical connection: myocarditis: inflammation of myocardium, because of viral infection/fever/radiation/chemicals, no symptoms (fever, fatigue, chest pain, irregular heartbeat, joint pain, breathlessness, endocarditis: inflammation of endocardium, heart valves. Left ventricle: thickest chamber of heart, forms apex, contains trabeculae carnae and chordae tendinae, aortic valve: blood passes from left ventricle to ascending aorta. Operation of semilunar valves: aortic and pulmonary valves called this because they are made of three moon shaped cusps, allow ejection of blood from heart into arteries, prevent backflow of blood into ventricles.