Cardiac cycle

The recurrent sequence of contraction and relaxation during a heartbeat. Electrical activity, mechanical contraction and sensory afferent signals have related but different timings.

During this stage of the cardiac cycle, the ventricular inlet and outlet valves are both closed. Ventricular volume is fixed at its end-filling value $V^{+}$, while increasing ventricular elastance raises pressure as $p_{LV}=E_{LV}(t)(V^{+}-V_0)$. Arterial and venous pressures remain approximately fixed when the stage is short relative to their systemic resistance–compliance times.

The relaxation and filling phase of a cardiac cycle. In cardiac-phase experiments it provides a comparison period with different baroreceptor signalling.

The contraction phase of a cardiac cycle; ventricular systole includes ejection of blood. Timing a stimulus to systole can change its relation to cardiovascular afferent signals.