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Heart and Circulation: Outside and Inside

Author(s): Ronald L. McNeel, DrPH, Barbara Z. Tharp, MS, Gregory L. Vogt, EdD, and Nancy P. Moreno, PhD
Heart and Circulation: Outside and Inside

© Peter Junaidy.

  • Grades:
  • Length: Variable


Students explore the human heart and circulatory system. To promote deeper understanding of key concepts, the activity also includes a procedure for observing preserved sheep hearts.

This activity is from the Scientific Decision-Making: Supplementary Activities on the Cardiovascular System, part of a teaching unit which includes the publication, Scientific Decision-making Teacher's Guide.

Teacher Background

The heart is a complex pump made of a special kind of muscle, called cardiac muscle, which is very resistant to fatigue. Although it is made of living cells, the heart shares many characteristics with mechanical pumps we see everyday.

A pump is a mechanical device that uses pressure or suction to move fluid or gas. For example, consider a liquid soap dispenser. A plastic tube extends from the dispenser’s top into the soap. When you depress the top, soap already in the tube squirts out. A one-way valve prevents any soap from flowing back down the tube. When you release the dispenser top, a spring-driven pump pushes it back up, while simultaneously “pulling” more soap from the bottle to refill the tube. It is important to note that for a pump to work, it must have a “pumping” mechanism and a one-way valve.

Bird and mammal hearts have two side-by-side pumps, and a total of four chambers. Two chambers, called atria, receive blood, and two chambers, called ventricles, pump blood out to the lungs and the rest of the body.

In the circulatory system, veins carry blood toward the heart, and arteries carry blood away from the heart. The large arteries that carry blood away from the heart divide into smaller and smaller vessels, called arterioles, until they become capillaries, the smallest blood vessels. Capillaries form a network between arteries and veins; they make oxygen and nutrients available to cells, and remove carbon dioxide and other wastes from cells. After passing through the capillaries, blood begins its journey back to the heart via small vessels, called venules. Venules combine into larger and larger vessels, called veins, and eventually become the major veins (inferior and superior vena cava) that enter the right atrium of the heart.

Circulation within the heart and body is described on the “Blood Pathways” sheet (see lesson PDF).

Objectives and Standards

Materials and Setup

Teacher Materials (see Safety)

  • Several copies of “Red Blood Cell Journey,” printed on card stock and cut into multiple sets (one set per student team)
  • Computer and projector, or an interactive white board if using video with students

If conducting dissection

  • Masking tape and straight pins (10 pins per student group)

Materials per Team of Students

  • Copies (one per student) of “The Heart: External,” “The Heart: Internal,” and “Blood Pathways” pages

  • Set of Red Blood Cell Journey cards

  • Copies of “Heart Guide: Outside and Inside” (copy for each student)

If conducting dissection, each group of students also will need:

  • 10 straight pins with masking tape flags, numbered 1 through 10

  • 2 pipe cleaners

  • Sheep heart (preserved)

  • Dissection kit (including scalpel and dissecting scissors)

  • Dissection tray (paper plates may be substituted)

If conducting dissection, each student also will need:

  • Dissection kit (including scalpel and dissecting scissors)

  • Pair of disposable plastic gloves

  • Pair of safety goggles

  • Personal copy of “Heart Guide: Outside and Inside”


  1. Copy or print the “Red Blood Cell Journey” sheet on card stock and cut into cards.

  2. Make individual copies of “The Heart: External,” “The Heart: Internal,” and “Blood Pathways,” student sheets.

  3. For the dissection activity, make individual copies of “Heart Guide: Outside and Inside,” for each student.

  4. Purchase sheep hearts ahead of time from a biological supply company (hearts are preserved and can be used for several weeks). Keep the sheep hearts in tightly sealed plastic bags and store under a ventilation hood, if possible. Place all necessary dissecting materials on paper plates or trays, with one set of materials for each student group. Prepare straight pins with masking tape flags for each group, or have students make their own. Have students perform the heart dissections in groups of two to four, or conduct the activity as a class demonstration.

  5. A video demonstration of a sheep heart dissection, including external and internal features of a mammalian heart, is available on BioEd Online at

  6. Have students work in groups of 2–4 for this activity.


  • Before beginning the heart dissection, instruct the students on the proper way to handle sharp instruments. All students should wear gloves and goggles. After the activity, sanitize all surfaces exposed to the heart, using a 10% bleach solution or commercial disinfecting spray. Refer to the Material Safety Data Sheet shipped with the hearts for instructions on the proper disposal of dissected sheep hearts. Students should wash their hands thoroughly with soap and water before and after any science activity, even if wearing gloves. Always follow all district and school laboratory safety procedures.

  • Commercial science education suppliers of dissection specimens are inspected by the United States Department of Agriculture to ensure that they comply with the Animal Welfare Act. Many specimens offered by suppliers originated in the food industry.

Procedure and Extensions

Time: One to three 45-minutes class periods

Part One. Heart and Circulation

  1. Ask students, Have you learned anything surprising about the heart so far? What do you think the heart looks like? After students have shared their ideas, tell them that they will be studying external and internal features of mammalian hearts. If your class is conducting the dissection, inform students that they will be observing preserved sheep hearts.

  2. Distribute copies of the student sheet, “The Heart: External,” to each student group. Explain that when looking at the diagram, students should imagine they are facing another person’s heart. This means that the side of the heart labeled “right” is on the left side as they face the diagram.

  3. Instruct students to locate the right side of the heart on the diagram. Next, have them find and label the corresponding area on the photograph. Within their groups, students should continue to locate and label on the photograph each part that is identified on the diagram. When students have finished labeling their heart diagrams, have them compare their work within their groups to check answers and discuss any discrepancies.

  4. Next, give each student a copy of “The Heart: Internal.” Direct students to identify and label the receiving areas (atria) and pumping areas (ventricles) of the heart on the diagram, and find and label the same structures on the photograph. Point out the valves and ask, What might the valves do? [prevent blood from flowing backward] Have students locate and label on the photograph each part that is identified on the diagram, and share their results as before.

  5. Conduct a class discussion about the internal structures of the heart, asking questions such as, Which chambers of the heart have thicker walls? [Ventricles] Why do you think ventricle walls are thicker than atrium walls? [Ventricles work harder to circulate blood around the body.]

  6. Inform students that having examined how blood flows into and out of the heart, they now will investigate how blood travels throughout the body. Provide each student with a copy of the “Blood Pathways” sheet, and have students read each numbered step to follow the path of blood around the body.

  7. Provide a set of Red Blood Cell Journey cards to teams of 2–4 students. Have students sort the cards into the same order as the blood circulation steps depicted in the “Blood Pathways” sheet. Then, have the teams mix up their cards. Challenge the teams to one or more races, to see which team can re-sort the cards into the correct circulation order most quickly. Start each race at a different point in the circulation path (e.g., “left ventricle” or “aorta”). The correct pathway (starting in the lungs) is given below.

    Capillaries in Lung →Pulmonary Veins →Left Atrium →
    Mitral (Bicuspid) Valve →Left Ventricle →Aortic Valve →
    Aorta →Arteries →Capillaries in Body →Veins →
    Superior and Inferior Vena Cava →Right Atrium →
    Tricuspid Valve →Right Ventricle →
    Pulmonary Valve →Pulmonary Arteries

  8. Use one of the following options to conclude Part One of this activity, either in class or as homework.

  • Have each student write an essay from the perspective of a red blood cell. Describe the blood cell’s path as it travels from a capillary in the left little finger, through the body, and back to the left little finger. Students may use the Blood Pathways page as a reference.
  • Have each student complete the “Draw the Heart” activity. Download the PowerPoint® file from the link below and work with students as they produce a basic drawing of the heart. (Set of slides was developed by the University of North Texas,
  • Use the virtual Sheep Heart anatomy interactive tool to enable students to examine a sheep heart ( Clicking on the sections provides different external and internal views. This tool was developed and copyrighted by J. Crimando, PhD, at Gateway Community College in Phoenix, Arizona.

Part Two. Outside of the Heart

Requires preserved sheep heart.

  1. Distribute copies of “Heart Guide: Outside and Inside” (one per team), and have one member of each team pick up supplies for the dissection.

  2. Have each team observe its preserved heart, following the “Heart Guide: Outside and Inside,” and complete "Part One: Outside the Heart," (see lesson PDF). You may want to point out the front, back, and bottom of the heart. The front is somewhat rounded; the back is flat, with openings where major vessels were attached. The bottom of the heart comes to a tip, or apex. After students are familiarized with the general orientation to the heart, teams should work independently from the teacher as much as possible. Students should refer to the diagram on “The Heart: External,” sheet to help locate the structures.

  3. When all of the labeling pins are in place, have teams switch hearts and crosscheck each other’s work to see if they agree with placement. If there is disagreement in the positioning, instruct the teams to resolve the differences by reexamining the diagrams.

  4. When step 3 is complete, have the students remove all pins and proceed to Part Three.

Part Three. Inside of the Heart

Requires preserved sheep heart

  1. Teams will follow and complete "Part Two: Inside the Heart," (see lesson PDF), of the Heart Guide student sheet. Students will open the sheep hearts through a series of cuts made by scissors or a scalpel. You may wish to demonstrate how to make the first cut into the heart, or simply complete this step for students. First, insert the point of a pair of dissection scissors or a scalpel into the superior vena cava (large vein that enters the right atrium, sometimes visible only as a large hole). Cut down the superior vena cava into the anterior wall of the right auricle and continue down to the apex. Students should be able to see the right atrium and ventricle.

  2. Students will make a second incision to open the left atrium and ventricle. You may wish to assist students with the incision. Insert scissors or knife into the pulmonary vein (may appear as a large hole) on the left side of the heart, and cut through the anterior wall of the left auricle. Once again, continue forward toward the apex.

  3. Have students refer to the diagram on “The Heart: Internal,” sheet to locate and pin the structures listed in Part Two of the Heart Guide.

  4. When all labeling pins are in place, have student teams switch hearts and crosscheck each other’s work to see if they agree with placement. If there is disagreement regarding pin positioning, instruct the teams to try to resolve the differences before involving the teacher.

  5. Have students discuss and demonstrate the flow of blood through their heart specimens, beginning with the point of entry at the superior vena cava. Direct students to push pipe cleaners through the large vessels to discover where they lead. To prevent punctures or damage to the hearts, have students bend the ends of the pipe cleaners back about an inch.

  6. Once students understand the flow of blood via heart-lung-heart-body circulation, explain that the right and left atria contract at the same time, followed by contractions of right and left ventricles. In a properly functioning heart, the synchronized work of the four chambers causes the atria to expand and fill with blood while the ventricles are contracting.

  7. Have teams clean and return all dissection equipment and remove, clean and return the numbered straight pins. Students should thoroughly clean their desktops and wash their hands with soap and water. Dispose of sheep hearts properly, and in accordance with school policy.

  8. After completing the activity, you may wish to assess students’ understanding of heart anatomy and movement of blood through the heart and body. This can be accomplished informally through a class discussion, or more formally by having students draw the dissected, labeled hearts in their science notebooks. Alternately, you may want to set up a lab practical assessment using heart specimens.

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