Basic Cardiology

The heart is a muscular pump approximately the size of your fist and its primary function is to pump oxygenated blood to the rest of the body. It is made up of four chambers, the right and left atria on the top, and the right and left ventricles on the bottom. The septum is a thin muscular wall that separates the right and left sides of the heart. Each contraction of the heart occurs in response to a carcontrical impulse that generates in the upper portion of the heart. Blood is moved in a closed circuit through the body by the pumping of the heart. The heart contracts and pumps blood out to the body (systole) and relaxes to fill with more blood (diastole).

The heart muscle itself is like all other organs in the body and requires oxygen to function. The oxygen-rich blood is circulated to the heart muscle through the coronary arteries. There are two main arteries: the right coronary artery and the left main coronary artery, both starting at the aorta (the main blood vessel of the body). These vessels then branch off into smaller and smaller vessels along the surface of the heart.

Electrophysiology

Click the image to see an animation on electrophysiology study.

The coronary veins and arteries are considered the plumbing of the heart, the conduction system can be considered the electrical wiring of the heart. Through this wiring, each muscle fiber of the heart knows when and how fast to beat so that the heart can pump efficiently.

The electrical system of the heart is greatly affected by the brain and by certain hormones and body chemicals called electrolytes. How these elements work with the rhythm generators of the heart determines the heart rate and sequence of the heartbeat. The sino-atrial (SA) node is the body's main natural cardiac pacemaker. The heartbeat starts here and spreads like the ripples in a pond throughout the network of conduction fibers in the two atria (the two upper chambers), causing them to contract. Normally, the heartbeat can only reach the ventricles (the two lower chambers) after it has passed through the atrioventricular (AV) node. The AV node slows down the electrical signal so that the atrial contractions can finish and fill the ventricles more completely. The AV node also prevents the lower chambers from beating too fast if the atria develop a fast rhythm (tachyarrhythmia). The electrical signal finally passes to the ventricles, the main work horses of the heart, through the bundle of His, bundle branches, and the Purkinje system (a specialized network of nerves that coordinates contraction of the ventricles). Each heartbeat is then completed and a new one is initiated in the SA node.

The heartbeat is an amazing combination of the heart's own natural rhythms and the brain's and body's requirements for energy. When you are nervous or exercising, the heartbeat accelerates; during relaxation, it slows.