Heart

The heart is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone. The heart pumps blood through the network of arteries and veins called the cardiovascular system.
The heart has four chambers:
1. The right atrium receives blood from the veins and pumps it to the right ventricle.
2. The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
3. The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
4. The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.

Irregular heartbeat

Heart rhythm problems (heart arrhythmias) occur when the electrical impulses in your heart that coordinate your heartbeats don't work properly, causing your heart to beat too fast, too slow or irregularly. Heart arrhythmias (uh-RITH-me-uhs) are often harmless. Most people have occasional, irregular heartbeats that may feel like a fluttering or racing heart. However, some heart arrhythmias may cause bothersome — sometimes even life-threatening — signs and symptoms.
Heart arrhythmia treatment can often control or eliminate irregular heartbeats. In addition, because troublesome heart arrhythmias are often made worse — or are even caused — by a weak or damaged heart, you may be able to reduce your arrhythmia risk by adopting a heart-healthy lifestyle.