Trying to remember the blood flow through the heart was always a difficult task when first learning it. Here I will explain the direction and process in the simplest way.
Initially, oxygen poor blood comes from the head and upper extremities, and enters the superior vena cava. While, blood from the lower extremities and everywhere else, enters the inferior vena cava.
After passing through the vena cava, the blood now enters the right atrium of the heart.
While exiting the right atrium, the oxygen poor blood then has to pass through the Tricuspid valve to reach the right ventricle. A simple way I use to remember the difference between the tricuspid valve and the mitral valve is “TRI it before you BI it”. Referring to the leaflets of the valves. Tricuspid valve has three leaflets (TRI) and the mitral valve has two leaflets (BI).
After reaching the right ventricle, the oxygen poor blood makes its way through the pulmonic valve, to the pulmonary arteries, where the blood is then taken to the lungs to get oxygenated before it is returned to the heart, through the pulmonary veins and into the left atrium.
From the left atrium, the blood passes through the mitral valve (bi) and into the left ventricle. Where the oxygenated blood then passes through the aortic valve, into the aorta, and then disperses the oxygen rich blood to the body.