Cardiology

Cardiology (from Greek καρδίᾱ, kardiā, "heart"; and -λογία, -logia) is a subspecialty of internal medicine dealing with disorders of the heart and blood vessels. The field includes diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians specializing in this field of medicine are called cardiologists. Cardiologists should not be confused with cardiac surgeons who are surgeons who perform cardiac surgery - operative procedures on the heart and great vessels.

The term cardiology is derived from the Greek word καρδιά (transliterated as kardia and meaning heart or inner self).

The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (Cardiac muscle). The myocardium contracts after stimulation. It is the ordered stimulation of the myocardium that allows efficient contraction of the heart, thereby allowing blood to be pumped throughout the body

Cardiac muscle has some similarities to neurons and skeletal muscle, as well as important unique properties. Like a neuron, a given myocardial cell has a negative membrane potential when at rest. Stimulation above a threshold value induces the opening of voltage-gated ion channels and a flood of cations into the cell. The positively charged ions entering the cell cause the depolarization characteristic of an action potential. Like skeletal muscle, depolarization causes the opening of voltage-gated calcium channels and release of Ca²⁺ from the t-tubules. This influx of calcium causes calcium-induced calcium release from the sarcoplasmic reticulum, and free Ca²⁺ causes muscle contraction. After a delay (the absolute refractory period), Potassium channels reopen and the resulting flow of K⁺ out of the cell causes repolarization to the resting state.

Note that there are important physiological differences between nodal cells and ventricular cells; the specific differences in ion channels and mechanisms of polarization give rise to unique properties of SA node cells, most importantly the spontaneous depolarizations necessary for the SA node's pacemaker activity .