The Nikon MicroscopyU confocal microscopy image gallery was created with a PCM-2000 confocal scanning system interfaced to a Nikon Eclipse E600 upright microscope. Images were recorded in successive z-axis serial sections with C-Imaging Systems software with excitation illumination provided by an argon-ion and/or a helium-neon laser.

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View a lower magnification confocal sequence of the heart thin section.

Shakespeare may have had some real insight into the autonomic nervous system when he said that "a merry heart goes all the day" in his Winter's Tale. The human heart is a muscle that is controlled by the sympathetic nervous system and is responsible for circulating the blood tissue.

The human heart, typical of mammals, is a four-chambered hollow muscular organ, found between the lungs and enclosed in the pericardium (cardiac) cavity. The average adult heart is about five inches in length and three and a half inches at its broadest part. Men typically have larger and heavier hearts than women. The heart is subdivided into chambers: a left and right auricle and a left and right ventricle.

Human hearts are not symmetrical with the right auricle being a little larger than the left, but having thinner walls. The right auricle holds about two ounces of blood and is subdivided into the atrium (or sinus venosus) and anterior, a smaller appendix auriculae, resembling a dog's ear in shape. Oxygen-depleted blood is carried by the superior vena cava from the upper half of the body and the inferior vena cava from the lower half, to the right auricle. Blood next enters the right ventricle and is then pumped via the pulmonary artery under pressure to the lungs for releasing carbon dioxide and receiving fresh oxygen. Fresh blood returns to the heart via the four pulmonary veins to the left auricle where it is then pumped to the longer left ventricle. Blood leaves the heart via the aorta that has a valve for use throughout the body.

During a severe heart attack, the heart muscle is injured from a lack of oxygen. Even though surviving heart muscle cells grow larger to compensate for losses, this only makes the heart more inefficient. Treatment for severe heart failure is limited to making the remaining heart work better or heart transplantation, since a person is born with all the heart cells that they will ever have. In cardiomyoplasty, skeletal muscles from the patient's back or abdomen are wrapped around the ailing heart and stimulated by a pacemaker-like device. In this case, the transplanted cells are not actually part of the heart, but mechanically assist its pumping actions. Current medical research is providing some hope that individual skeletal muscle cells (myoblasts) or stem cells from umbilical cord blood may be capable of actually regenerating dead heart muscle during transplants.