Blood Flow through the Canine Heart

     The canine heart ranges between 0.6 - 0.9 percent of the dog's body weight. Located within the chest cavity, the heart's base lays closer to the spinal cord while its apex lays closer to the sternum. Similar to the human heart, the canine heart is composed of four chambers. The upper chambers are the left atrium and right atrium, which serve as the receiving chambers for the blood. The lower chambers are the left and right ventricles, which serve as muscular pumps to circulate the blood.
     Each chamber consists of dividing walls (septa) and one-way valves. These valves assure that the blood will flow forward during normal cardiac activity. The heart valves fall into two types; artrioventricular (A-V) and semilunar valves.
     The A-V valves are located within the chamber wall which separates the atria from the ventricles. These valves open whenever a ventricle relaxes, enabling the blood to flow into the ventricle. The valves close as the ventricle contracts, thereby preventing a backflow of blood into the atrium. The A-V valve on the right side of the heart is the tricuspid valve. The A-V valve on the left side of the heart is the mitral valve.
     The Semilunar valves separate each ventricle from its corresponding great artery (either aorta or pulmonary artery). The semilunar valve opens when the ventricle contracts, enabling bloodflow into the artery and closes when the ventricle relaxes, thus eliminating backflow from the artery into the ventricle. The semilunar valve on the right side of the heart is the pulmonic valve. The semilunar valve on the left side of the heart is the aortic valve.
     In putting the pieces together the blood circulates through the heart as follows:
Left side of heart
Step 1: left ventricle relaxes
           mitral valve opens
           blood flows from left atrium through mitral valve into left ventricle
Step 2: left ventricle contracts
           mitral valve closes
           aortic valve opens
           blood is propelled by ventricle contraction into aorta and enters systemic circulation

     With the relaxation of the left ventricle the aortic valve closes, the mitral valve opens and the process is repeated.

     Blood circulated through the left side of the heart is oxygen laden. From the aorta the oxygen laden blood will flow through the arteries and arterioles of the aterial circulatory system until it eventually reaches the capillary beds, where it releases the oxygen to the surrounding tissue. The blood is now picked up by the venous system, carried by venules and veins to the right side of the heart.

Right side of the heart
Step 1: right ventricle relaxes
            tricuspid valve opens
            blood flows from right artrium through tricuspid valve into right ventricle
Step 2: right ventricle contracts
            tricuspid valve closes
            pulmonic valve opens
            blood is pumped through pulmonic valve into the pulmonary artery

      With the relaxation of the right ventricle the pulmonic valve closes, the tricuspid valve opens and this process is repeated.

     From the pulmonary artery the blood is carried to he lungs where it picks up its oxygen load and is carried to the left side of the heart, thus completing its circuit.

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