Lead II is the limb lead that will show the best view of atrial depolarization. Remember, atrial depolarization starts at the sinoatrial node in the right atrium and spreads through the right and left atria. If you were to draw this on a heart, the net vector would be down (inferiorly) and to the left side of the heart. Also remember, lead II is the lead configuration that runs from the right arm to the left leg. aVR would show a good view of atrial depolarization (although it would be a negative deflection), but it is an augmented lead, not a limb lead. aVL is also an augmented lead.

The heart has four chambers. During diastole the atria contract to push blood into the ventricles, which are relaxed, but during systole the atria relax to fill with blood while the ventricles contract. This alternating contraction moves blood through the heart, the pulmonary circulatory path, and eventually out of the heart.

When the atria contract during diastole, blood is moving into the right ventricle and also into the left ventricle. During systole when the ventricles contract, blood is moving from the right ventricle towards the pulmonary circuit and from the left ventricle to the rest of the body.

The P wave represents atrial depolarization. The QRS complex represents ventricular depolarization, the T wave represents repolarization, and the U wave (if present) represents late ventricular repolarization (e.g. repolarization of bundle branches). There are no X waves on an EKG.

The average (normal) blood pressure is approximately 120/80. The first number represents the systolic pressure which is caused when the blood is forced out of the left ventricle and the aortic valve opens. The second number is the diastolic pressure and it occurs when the aortic valve closes and the ventricle relaxes. The device used to measure blood pressure is called a sphygmomanometer.

Cardiac output tells us the volume of blood pumped by each ventricle every minute. As a result, the two factors that we need to consider are the number of times that the heart beats every minute (heart rate), and the amount of blood pumped by each ventricle every beat (stroke volume). These two factors are multiplied in order to determine the cardiac output of the heart.

The pathway starts with sinoatrial (SA) node. It is the pacemaker of the heart and when a person has an artificial pacemaker installed it usually because of a malfunction at this node. The SA node releases electrical impulse regularly which spread in waves. Upon reaching the atrioventricular node, there is a small delay in reaction to allow for blood to be emptied from the atria. After they do empty, the impulse travels through the bundle of His and splits into the left and right bundles, which then lead to Purkinje fibers. These bundles split the signal to the left and right sides of the heart and the Purkinje fibers end in the walls of the ventricles.

The heart wall is made of three layers. The epicardium is the outer layer. The myocardiumis 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.

Ejection fraction is the percentage of blood pumped out of the left ventricle, in comparison to its volume when completely filled. Ejection fraction can be found by dividing stroke volume by end distolic volume. The other information given is excess and unnecessary.

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 tricuspid (atrioventricular) valve separates the right atrium from the right ventricle and prevents back-flow during systole (heart contraction). The path of blood in the heart goes as follows: right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary vein, left atrium, mitral valve, left ventricle, aortic valve, aorta, systemic circulation.