These atrio-ventricular valve flaps are anchored against eversion into the atria by the chordae tendinae, which are themselves attached to the papillary muscle. The left ventricle wall is much thicker, and pumps the systemic blood at a much higher pressure than in the pulmonary. The right ventricle's lower pressure minimizes damage to the alveoli and other thin walled elements of the lung. The intra ventricular septum is the wall of muscle between the two ventricles. On the outside of the heart are the auricles, or ear-like flaps above the atria, as are the coronary arteries and veins, vessels which provide flow of blood to sustain the heart muscle itself.
Cardiac output varies with stroke volume and heart rate.
The blood flow through the body depends on the pressure created and the resistance to the flow. Changes in the resistance are the usual mechanism for directing blood to various organ systems in varying degrees. The arterioles can vasoconstrict or vasodilate, allowing less blood or more blood, respectively, to flow through. During exercise, many parameters of the heart cycle change. The heart rate increases dramatically, paralleled by increases in stroke volume, though the stroke increases much less than the rate.