 Dr. O. In this short video, I want to cover the cardiac cycle. So before we start, you have to know a couple of terms, systole versus diastole. So systole means contraction, diastole means relaxation. So hopefully those terms are a little bit familiar to you because of your blood pressure. If your blood pressure is 120 over 80, that is your systolic blood pressure over your diastolic blood pressure. So that's why these terms are important. Systole means contraction. So your systolic blood pressure is the pressure as the blood is actively flowing through your circulatory system. Diastolic blood pressure is when it's resting. So we'll cover blood pressure in this other video. So the cardiac cycle is a combination of systole and diastole. So we have atrial systole would be when your two atria are contracting. Remember that most of the ventricles are going to fill on their own. So about 20% of the ventricular filling is going to happen when the atria contracts. So atrial systole, what's happening then is it's going to top off the tank and help fill the ventricles. Then we have ventricular systole is when your two ventricles are contracting. The right ventricle is going to send blood through the pulmonary circuit to your lungs and back. The left ventricle is going to send blood through your systemic circuit everywhere else. So that's going to be what happens during systole. And then each of those is going to take turns resting. So during ventricular systole, you'll have atrial diastole, where the atria are relaxing and refilling with blood. And then during atrial systole, that's when your ventricles are relaxing and ventricle diastole. All right, so here we just see again, cardiac diastole is when the whole heart is resting for a set split second there. During atrial systole, your ventricles are relaxing as they're filling with blood. During ventricular systole, while the ventricles are pumping blood, the atria are relaxing and filling with blood. And then it happens again. And again, you know, 75 times every minute. So that's the cardiac cycle. I hope this helps. Have a wonderful day. Be blessed.