70% venous system, 15% heart and lungs, 10% arterial system, 5% capillary exchange. Blood to individual muscles can increase as much as 20-fold. Mitral valve left heart, between the atrium and ventricle. Aortic valve left heart tricuspid valve . Mitral and tricuspid are referred to as the antriventricular valves while the aortic and pulmany valves are often referred to as the semilunar valves. In syncytium: atrial syncytium and ventricular syncitium. Seperated by fibrous tissue called the atrioventricular ring. Potassium declines during diastole while the permeability for other ions does not change. Prepotential: na+ goes through funny channels and ca++ through t-type channels. Repolarization: calcium channels closing and potassium opening. Rate can be altered by changing the slope of the prepotential or the resting" mp. Sa node activity spreads through internodal pathway and through interatrial myocardial band to left atrium. Then goes to av node, bundle of his and to purkinje fibers.