The conditions
An arrhythmia is a variation in the heartbeat. It can become faster or slower than usual, or become irregular. Sometimes, an arrhythmia can stop the heart from pumping enough blood around the body, including to the brain and heart muscle. This can happen very suddenly and unexpectedly, leading to sudden death, and is usually caused by 'fast' arrhythmias in the ventricles (the lower chambers of the heart). Congenital heart disease is a heart problem that someone has been born with.
Heart failure can be caused by several things that make the heart a less efficient pump. When the left ventricle of the heart pumps less blood to the body because of weak contractions, it is called left ventricular dysfunction.