Heart pushes and pulls blood in and out through the veins and arteries. One direction carries blood with oxygen, one brings it back with CO2. The lungs play an important part of this. Remember kids, stay in school, and do homework to learn, not to recite.

Blood enters the heart through the vena cava. From here it moves into the right atrium and then down into the left ventricle and up the pulmonary artery to the lungs where carbon dioxide is switched for 'fresh oxygen'. The blood is returned to the heart via the pulmonary veins which guides the blood into the left atriun where it moves down to the left ventricle. From here it is pumped via the aorta all around the body

The late great Jeff Buckley said it better than anyone else ever has. "A heart that beats as both siphon and reservoir."

Start>Left Atrium>Bicuspid>Left Ventricle>Aortic Semi-Lunar Valve>Aorta>Arteries>Arterioles>Capillaries>Venules>Veins>Superior/Inferior Vena Cava>Right Atrium>Tricuspid>Right Ventricle>Pulmonary Semi-Lunar Valve>Lungs>Left Atrium.

As blood flows through the body, it gives oxygen to the tissues and receives CO2 plus other waste products from those tissues. The de-oxygenated blood enters the right atrium through the superior (top), inferior (bottom), The bodies largest veins, and the coronary sinus which is rarely mentioned. The right atrium contracts, forcing (pumping) blood through the tricuspid valve and into the right ventricle. The right ventricle contracts, sending blood through the pulmonary semilunar valve and into the pulmonary trunk. The pulmonary trunk divides into pulmonary arteries (one for each lung), which takes the deoxygenated blood to the capillaries of the lungs. At the lungs, carbon dioxide diffuses out of the blood, and, oxygen diffuses into the blood. The capillaries is where oxygen enters the blood stream. The oxygenated blood feeds into the pulmonary veins, which take it from the lungs to the left atrium. The left atrium contracts, forcing blood through the bicuspid (mitral) valve and into the left ventricle. The left ventricle contracts, forcing (pumping) blood through the aortic semilunar valve into the aorta, the bodies largest artery. The aorta divides into smaller arteries, which carry oxygenated blood to all body tissues. And the cycle is repeated. Note that deoxygenated blood never mixes with oxygenated blood. In reality, the events described above don't happen in a linear sequence. Instead, the two atria and the two ventricles contract simultaneously. I hope this has answered your question.

superior "slash" inferior vena cava> right atrium> tricuspid valve> right ventricle> "pulmonary trunk"> pulmonary valve> pulmonary artery> lungs > left atrium> bicuspid valve> left ventricle> aorta> body

right atrium to the right ventricle to the left atrium to the left ventricle(DUH)