sístole

Sístole (systole) is the phase of the cardiac cycle during which the heart muscle contracts and blood is ejected from the ventricles into the aorta and pulmonary artery. It follows diastole and, together with diastole, forms the cardiac cycle. The term is often paired with its English equivalent, systole, and is contrasted with diastole, the filling phase.

Two components are commonly described: atrial systole and ventricular systole. Atrial systole contributes to ventricular filling by contracting the atria near the end of diastole. Ventricular systole is the main phase of blood ejection, beginning after the atrioventricular valves close and ending with the closure of the semilunar valves. During ventricular systole, the heart passes through an isovolumetric contraction phase, when pressures rise but all valves are closed, followed by the ejection phase as the semilunar valves open.

Physiologically, systolic events are reflected in arterial pressure as the systolic blood pressure, the peak pressure during this phase. The duration of systole is typically about 0.3 seconds in a healthy adult at rest, representing roughly one third of the cardiac cycle; the remaining time is diastole, which lengthens at lower heart rates and shortens as heart rate increases. Electrical activity correlates with systole: ventricular depolarization (the QRS complex on the electrocardiogram) precedes the onset of ventricular systole.

Clinical relevance includes conditions affecting systolic function, such as systolic heart failure, where contraction is reduced, and systemic or pulmonary systolic hypertension, where peak pressures are elevated. Measurements include ejection fraction, stroke volume, and noninvasive blood pressure monitoring to assess systolic performance.