Cardiac pacemaker Cardiac pacemaker The contraction of cardiac muscle (heart muscle) in all animals is initiated by electrical impulses known as action potentials. The rate at which these impulses fire controls the rate of cardiac contraction, that is, the heart rate. The cells that create these rhythmic impulses, setting the pace for blood pumping, are called pacemaker cells, and they directly control the heart rate. They make up the cardiac pacemaker, that is, the natural pacemaker of the heart. In most humans, the concentration of pacemaker cells in the sinoatrial (SA) node is the natural pacemaker, and the resultant rhythm is a
Heart failure acute respiratory distress. High-output heart failure can occur when there is an increased cardiac output. The circulatory overload caused, can result in an increased left ventricular diastolic pressure which can develop into pulmonary congestion (pulmonary edema). Heart failure is divided into two types based on ejection fraction, which is the proportion of blood pumped out of the heart during a single contraction. Ejection fraction is given as a percentage with the normal range being between 50 and 75%. The two types are: 1) Heart failure due to reduced ejection fraction (HFrEF). Synonyms no longer recommended are "heart failure due to