Systole and Diastole – Cardiac Cycle

00:02 The cardiac cycle.

00:04 Here in the cardiac cycle, we need to break it down into its two most basic forms – that is systole and diastole.

00:13 So, in terms of systole, what really are we talking about? We’re talking about what's occurring with ventricular contraction.

00:20 So, contraction is one of the biggest components of systole.

00:25 Interestingly, though, also, is the ejection of blood comes along with contraction.

00:31 So, the majority of the time, during the ejection phase of the blood, there will be within systole.

00:40 However, a little bit of it translates over into diastole.

00:46 There is a relaxation phase that transitions between systole and diastole.

00:52 So, what do I mean by relaxation? It is the muscles themselves – cardiac muscle – that is relaxing.

01:00 So, it's interesting to think about, even when the muscle is relaxing a little bit, you still could be in systole, i.e. pushing blood out because blood being pushed out of the left ventricle is simply a matter of the pressure differential.

01:16 The other times in which you are in diastole are during the filling phases.

01:21 And you notice we have some numbers attached to things like ejection and filling.

01:27 That is because there's a rapid and a reduced ejection and a rapid and a reduced filling.

01:35 So, all of those kind of items come out when we look at the cardiac cycle.