The  atrioventricular nodal delay helps the heart pump blood efficiently in one direction. The atrioventricular node slows electrical current sent by the sinoatrial node, before this signal is allowed to propagate down to the ventricles. This delay ensures that the atria have the time to fully empty all blood contents into the ventricles, before ventricular contraction takes place. The atrioventricular nodal delay also prevents the atria and ventricles from contracting against each other. 

Ventricular blood volume should be lowest during the T wave of a healthy patient's electrocardiogram. This is because the T wave represents ventricular repolarization, which occurs after the ventricles have contracted and ejected their blood into the pulmonary and systemic circulation. 

The heart wall is made of three layers. The epicardium is the outer layer. The myocardium is the middle, muscular layer that accounts for the contractibility of the heart via pumping action. The endocardium is the inner layer that lines the cavities of the heart. The parietal pericardium consists of an inner layer of serous membrane. The perimysium is the outtermost connective tissue of a muscle. 

Both the superior vena cava and inferior vena cava drain into the right atrium. Blood leaves the right heart through the pulmonary trunk. Blood enters the left heart through the left and right pulmonary veins. Blood leaves the left heart via the aorta. 

The pulmonary veins carry oxygen-rich blood from the lungs to the left atrium. Veins carry blood towards the heart, whereas arteries carry blood away from the heart. The superior and inferior vena cavae drain into the right atrium. The aorta distributes oxygen-rich blood to the systemic circulation.  

Cardiac output is the amount of blood pumped by blood per minute. This can be measured by the equation: .  Ejection fraction is represented by: . Stroke volume is represented by the equation: . Pulse pressure is represented by the equation: .

Cardiac output is the amount of blood pumped by the heart per minute. The 4 factors that are important in determining cardiac output are preload, afterload, heart rate, and myocardial contractility. The first heart sound occurs at the onset of ventricular systole and is due to the closure of the atrioventricular valves. 

The first heart sound (s1) is due to the closure of the atrioventricular valves. This occurs at the onset of ventricular systole since, the ventricles are contracting and will eject blood through the pulmonary trunk and aorta.

The tricuspid valve is the right AV valve. The left AV valve is referred to as the bicuspid, or mitral valve. Thus, these two names represent the same structure. The semilunar valves are responsible for guarding the exits from the two ventricles. 

The fetal heart differs from and adult heart because there is a hole or foramen in the wall separating the atria that allows blood to pass through. Its purpose is to allow the fetus to receive oxygenated blood and in essence bypass the pulmonary circuit, by allowing blood to enter from the right atrium into the left atrium. Also, the fetal circulatory system includes the ductus arteriosus, which shunts blood from the pulmonary trunk to the aorta, again bypassing the pulmonary circuit. Both of these structures close at birth, once the newborn's lungs have been exposed to air. The ductus arteriosus is subsequently called the ligamentum arteriosus.