During diastole in the cardiac cycle, what primarily happens?

During diastole in the cardiac cycle, what primarily happens?

• A. The heart contracts and ejects blood.
• B. The heart muscle relaxes and chambers fill with blood.
• C. Blood is ejected into the arteries.
• D. Electrical conduction speeds up.

Answer: (B)

During diastole, the heart muscle relaxes and the chambers fill with blood. As the ventricles relax, the atrioventricular valves (the mitral and tricuspid) are open, letting blood flow from the atria into the ventricles. Most filling happens passively, and toward the end of diastole the atria contract a bit more to top off the ventricles. The semilunar valves stay closed during this phase, preventing blood from flowing back into the ventricles and preparing the heart for the next heartbeat. This contrasts with systole, when the ventricles contract and eject blood into the arteries. The idea of blood being ejected into the arteries is a systolic event, not diastolic. Electrical conduction speed is not the defining feature of diastole; it relates to how the heartbeat is coordinated, but diastole is defined by relaxation and filling.

During diastole, the heart muscle relaxes and the chambers fill with blood. As the ventricles relax, the atrioventricular valves (the mitral and tricuspid) are open, letting blood flow from the atria into the ventricles. Most filling happens passively, and toward the end of diastole the atria contract a bit more to top off the ventricles. The semilunar valves stay closed during this phase, preventing blood from flowing back into the ventricles and preparing the heart for the next heartbeat.

This contrasts with systole, when the ventricles contract and eject blood into the arteries. The idea of blood being ejected into the arteries is a systolic event, not diastolic. Electrical conduction speed is not the defining feature of diastole; it relates to how the heartbeat is coordinated, but diastole is defined by relaxation and filling.