The Human Heart and Its Cardiac Cycle

The cardiac cycle describes three phases of a single heartbeat:

  • Phase 1 (diastolic). Ventricular filling occurs during the diastolic phase. Blood moves passively (70%) (as the tricuspid and mitral valves open) and by atrial contraction (30%) from the atria into the right and left ventricles.
  • Phase 2 (systolic). For a brief instant, the heart closes all of its valves and begins to create a forceful contraction (called an isovolumetric contraction). This is followed immediately by systolic ejection of blood through the aorta and pulmonary semilunar valves into the systemic (entire body except lungs) and pulmonary (lungs) arteries.
  • Phase 3. For only a brief moment, the heart closes all valves and goes into relaxation (called isovolumetric relaxation). It then repeats the cardiac cycle beginning at Phase 1.

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Len Kravitz, PhD

IDEA Author/Presenter
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University ... more less

Colin Carriker, MS

IDEA Author/Presenter

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