As a demonstration, dissect a fresh beef or pork heart. You can frequently obtain fresh materials from butchers at little or no cost. Ask them to leave the major blood vessels intact.
Show students the exterior features of the heart, including coronary vessels, auricles, and the major arteries and veins leading to and from the heart. Then cut the heart in half lengthwise. Show students the chordae tendinae (heart strings), atrioventricular valves, and aortic semilunar valve. Discuss the thickness of the muscle in the walls of individual heart chambers as it relates to the function of the chamber.
A variety of factors influence blood pressure. Certainly as people are more active, their blood pressure increases. As they return to rest, or go to sleep, blood pressure falls. Under stress, peripheral blood vessels constrict, increasing blood pressure. The factors that influence blood pressure are heart action, blood volume, the thickness or viscosity of blood, and its resistance to flow.
Divide your class into groups. Show students from each group how to measure arterial blood pressure using sphygmomanometers. Also show them how to measure heart rate in beats per minute. Have a volunteer or two from each group have their blood pressure and heart rate measured. Then ask these volunteers to run in place or perform jumping jacks until they feel slightly winded. Measure blood pressure and heart rate once again. Tabulate results on the chalkboard.