This a simple anatomy question. The mitral (bicuspid) valve lies between the left atrium and ventricle, therefore the answer must be the mitral valve. The tricuspid valve lies between the right atrium and ventricle.

The valve between the right atrium and ventricle is the tricuspid valve. The valve between the left atrium and ventricle is called the bicuspid, or mitral, valve. "Bicuspid" and "mitral" can be used interchangeably.

The pulmonary valve connects the right ventricle with the pulmonary artery, while the aortic valve connects the left ventricle with the aorta.  

The semilunar valves refer to the aortic valve and pulmonary valve, both of which have three flaps. The atrioventricular valves separate the atria from the ventricles. The right side of the heart is separated by the tricuspid valve, while the left is separated by the bicuspid, or mitral, valve. The mitral valve is the only heart valve with two flaps.

When blood passes from the right atrium into the right ventricle, it must pass through the tricuspid valve.

The mitral, or bicuspid, valve separates the left atrium and ventricle. The semilunar valves are the aortic and pulmonary valves. The aortic valve separates the left ventricle and aorta, while the pulmonary valve separates the right ventricle and pulmonary arteries.

After axons from the sinoatrial node flow through the atria to cause atrial contraction, the depolarization pauses in the atrioventricular node. Once the atrioventricular node depolarizes, the electrical signal travels though the bundle of His to the walls of the ventricles via purkinje fibers. The atrioventricular node initiates ventricular contraction, the bundle of His carries the signal, and the purkinje fibers allow for synchronized contraction of different regions of the ventricular wall.

The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.

The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.

The heart beats automatically through stimulation from the sinoatrial node. The group of neurons found in this node depolarize in a coordinated, spontaneous manner to allow for the contraction of the atria and ventricles in the heart. Without the sinoatrial node, heart contraction may be possible, but it would not be regular and would require additional regulation.

Depolarization of the sinoatrial node specifically leads to atrial contraction. The signal is then transmitted through the atrioventricular node and bundle of His to the purkinje fibers, which coordinate the contraction of the ventricles.

In a fetus, there are three fetal shunts: the ductus arteriosus, the ductus venosus, and the foramen ovale. Failure to fully close the foramen ovale during birth will allow blood to shunt directly from the right atrium to the left atrium, diverting the blood from the lungs. The ductus arteriosus also shunts blood away from the fetal non-functional lungs, allowing it to pass directly from the pulmonary artery to the aorta. Additionally, after birth, the ductus arteriosus becomes the ligamentum arteriosum.

Conversely, the ductus venosus is a structure in the fetus that diverts blood away from the fetal liver.

The left atrium has a higher pressure than the right atrium. As a result of the hole between the atria, there will be a left-to-right shunt of blood in the heart. Blood would normally go from the left atrium into the left ventricle. The shunt will allow blood from the left atrium to return to the right atrium, instead of proceeding to the left ventricle. Because of the shunt, less blood will go into the left ventricle.

There are four principle heart valves, each classified as either an atrioventricular (AV) valve or a semilunar valve. The atrioventricular valves separate the atria from the ventricles, while the semilunar valves separate the ventricles from arteries.

The tricuspid valve prevents backflow between the right atrium and right ventricle. The bicuspid, or mitral, valve prevents backflow between the left atrium and left ventricle. The pulmonary semilunar valve separates the right ventricle from the pulmonary artery, and the aortic semilunar valve separates the left ventricle from the aorta.