Cardiac Cycle
The contraction and relaxation of the heart’s musculature is highly coordinated during the cardiac cycle.
What our notes say
- The contraction and relaxation of the heart’s musculature is highly coordinated during the cardiac cycle. (Cardiovascular system examination revised 2012 — Past Paper Questions & Answers)
- There are 4 heart sounds produced during each cardiac cycle. (Medical Physiology Assorted SAQs — With Answers (Past Paper Study Guide))
- Events of the cardiac cycle include - phase I (atrial contraction), phase II (isovolumic ventricular/Isometric) contraction, phase III (ventricular systole – period of ejection), phase IV (isovolumic ventricular/Isometric) relaxation and phase V (Cardiovascular system examination revised 2012 — Past Paper Questions & Answers)
- QT interval — start ventricular depolarization → end ventricular repolarization; inversely proportional to heart rate (faster HR → shorter QT); ≈40% of the cardiac cycle (CVS History & Physical Exam: Symptoms, Chest Pain & Syncope)
- Shortened cardiac cycle: Reduced diastolic filling time (Medical Physiology II (Paper 2))
Study material on Cardiac Cycle
Practice questions on Cardiac Cycle
During which phase of the cardiac cycle do the aortic and pulmonary valves open?
- Atrial systole
- Isovolumetric contraction
- Ventricular ejection
- Isovolumetric relaxation
Answer: C. The aortic and pulmonary valves (semilunar valves) open during ventricular ejection. This phase begins when the pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery, forcing blood out of the ventricles. Atrial systole (A) is when atria contract. Isovolumetric contraction (B) is when ventricular pressure rises, but all valves are closed. Isovolumetric relaxation (D) is when ventricular pre