In the human heart, what is the name of the valve located between the left atrium (left auricle) and the left ventricle?

Introduction / Context:
The human heart contains four major valves that ensure blood flows in one direction through its chambers and into the major arteries. Correctly naming these valves and their positions is an important part of understanding circulatory physiology and is widely tested in biology and medical entrance exams. This question focuses on the valve that guards the opening between the left atrium and the left ventricle.

Given Data / Assumptions:

We are dealing with the left side of the heart. The valve is situated between the left atrium (left auricle) and the left ventricle. Options include mitral, tricuspid, semilunar, pulmonary and Eustachian valves. We assume normal human heart anatomy with four chambers and four main valves.

Concept / Approach:
The valve between the left atrium and left ventricle is called the mitral valve, also known as the bicuspid valve because it has two cusps or flaps. It opens to allow oxygenated blood from the left atrium to pass into the left ventricle during diastole and closes during ventricular systole to prevent backflow. The tricuspid valve lies between the right atrium and right ventricle. The semilunar valves (aortic and pulmonary) are located at the exits of the ventricles into the major arteries. The Eustachian valve is a small fold in the right atrium near the opening of the inferior vena cava and is not a major functional valve in adults.

Step-by-Step Solution:
Step 1: Visualise the four chambers of the heart: right atrium, right ventricle, left atrium and left ventricle. Step 2: Recall that atrioventricular valves lie between atria and ventricles; there are two such valves. Step 3: The tricuspid valve is on the right side between the right atrium and right ventricle. Step 4: Therefore, the valve on the left side between the left atrium and left ventricle must be the mitral or bicuspid valve. Step 5: Confirm that semilunar valves are located at the origins of the aorta and pulmonary artery, not between atria and ventricles.

Verification / Alternative check:
One way to verify is to link the valve names with typical heart diseases. Mitral valve prolapse and mitral stenosis involve the left atrioventricular valve, indicating that the mitral valve is indeed on the left side. Tricuspid valve diseases affect the right side of the heart. Additionally, remember the mnemonic that bicuspid and mitral both begin with letters indicating the left side in some study guides, helping you remember that the bicuspid or mitral valve is left sided. These associations confirm that the mitral valve lies between the left atrium and left ventricle.

Why Other Options Are Wrong:
The tricuspid valve is not on the left side of the heart; it is between the right atrium and right ventricle. The semilunar aortic valve is located at the junction of the left ventricle and the aorta, not between the atrium and ventricle. The pulmonary valve lies between the right ventricle and the pulmonary artery. The Eustachian valve is a small remnant structure near the opening of the inferior vena cava into the right atrium and does not represent a major functional heart valve in adults. Thus, these options do not match the anatomical location described in the question.

Common Pitfalls:
A common error is to mix up tricuspid and bicuspid valves because both are atrioventricular valves and have similar sounding names. Students sometimes guess tricuspid for any atrioventricular position without carefully distinguishing left from right. To avoid this, remember a simple link: tri for three flaps on the right side and bi for two flaps on the left side. Repeating the phrase tricuspid right, bicuspid left during revision can help lock in the correct associations.

Final Answer:
The valve present between the left atrium (left auricle) and left ventricle is the mitral (bicuspid) valve.