The cardiovascular system consists of the heart, which is an anatomical pump, with its intricate conduits (arteries, veins, and capillaries) that traverse the whole human body carrying blood. The blood contains oxygen, nutrients, wastes, and immune and other functional cells that help provide for homeostasis and basic functions of human cells and organs. [1, 2]
The pumping action of the heart usually maintains a balance between cardiac output and venous return. Cardiac output (CO) is the amount of blood pumped out by each ventricle in one minute. The normal adult blood volume is 5 liters (a little over 1 gallon) and it usually passes through the heart once a minute. Note that cardiac output varies with the demands of the body. 
The cardiac cycle refers to events that occur during one heart beat and is split into ventricular systole (contraction/ejection phase) and diastole (relaxation/filling phase). A normal heart rate is approximately 72 beats/minute, and the cardiac cycle spreads over 0.8 seconds. The heart sounds transmitted are due to closing of heart valves, and abnormal heart sounds, called murmurs, usually represent valve incompetency or abnormalities. 
Blood is transported through the whole body by a continuum of blood vessels. Arteries are blood vessels that transport blood away from the heart, and veins transport the blood back to the heart. Capillaries carry blood to tissue cells and are the exchange sites of nutrients, gases, wastes, etc. 
The heart is a muscular organ weighing between 250-350 grams located obliquely in the mediastinum. It functions as a pump supplying blood to the body and accepting it in return for transmission to the pulmonary circuit for gas exchange.
The heart contains 4 chambers that essentially make up 2 sides of 2 chamber (atrium and ventricle) circuits; the left side chambers supply the systemic circulation, and the right side chambers supply the pulmonary circulation. The chambers of each side are separated by an atrioventricular valve (A-V valve). The left-sided chambers are separated by the mitral (bicuspid) valve, and right-sided chambers are divided by the tricuspid valve. Blood flows through the heart in only one direction enforced by a valvular system that regulates opening and closure of valves based on pressure gradients (see image below).
Coronary circulation is the circulation to the heart organ itself. The right and left coronary arteries branch from the ascending aorta and, through their branches (anterior and posterior interventricular, marginal and circumflex arteries), supply the heart muscle (myocardial) tissue. Venous blood collected by the cardiac veins (great, middle, small, and anterior) flows into the coronary sinus. Delivery of oxygen-rich blood to the myocardial tissue occurs during the heart relaxation phase (see the image below).
Congenital heart anomalies Congenital heart defects cause structural problems of the heart and lead to abnormal or incomplete development of its major chambers and valves, resulting in poor flow and circulation.
Atrial septal defect is a hole in the wall between the right and left atria that promotes mixing of oxygenated and unoxygenated blood. See the image below.
Congestive Heart Failure
This is a clinical syndrome that results from the inability of the heart to pump effectively to achieve the cardiac output capable of supplying sufficient oxygen to the peripheral organs for basic metabolic function as well as metabolic demand. Heart failure may be further classified into right ventricular failure, left ventricular failure, or biventricular failure. Some of the main etiologies of congestive heart failure are as follows:
Valvular heart disease
Pulmonary arterial hypertension
High output states such as thyrotoxicosis, anemia or AV fistula.