By which week are the four heart chambers formed?

• A. 6th Week
• B. 8th Week
• C. 10th Week
• D. 12th Week

Answer: (B)

Heart development starts as a simple tube in the early weeks and then undergoes looping and septation to create separate chambers. The separation of the atria and ventricles is driven by the formation of the atrioventricular cushions and the growth of septa that divide the heart into right and left sides. This process continues through weeks 4 to 7, and by the end of the eighth week the heart has four distinct chambers—the right and left atria and the right and left ventricles. That timing explains why the four-chambered heart is considered formed by the eighth week. Earlier weeks show the heart as a single tubular structure or ongoing partitioning, not yet fully separated into four chambers.