Difficulty: Beginner to Intermediate | Prerequisites: Part 1 of this series (Cerebrovascular and Coronary Conditions), basic heart anatomy.
This section covers what can go wrong with the heart itself, from structural defects present at birth to conditions that develop over a lifetime, plus the vital signs and measurements clinicians use to assess cardiac function. If Part 1 was about the pipes (blood vessels), this part is about the pump (heart), the fluid dynamics (blood pressure, ejection fraction), and the systemic risk factors (diabetes, oedema) that make everything worse. These terms appear across cardiology, emergency medicine, and paediatrics exam questions.
The heart has its own electrical system, can be born with structural defects, and can gradually lose its ability to pump effectively. Clinicians measure how well it is working using ejection fraction, blood pressure readings, and imaging. Diabetes, oedema, and cyanosis are warning signs that the cardiovascular system is under strain. Know the difference between congenital and acquired conditions, and understand what ejection fraction and diastolic pressure actually measure.
Conduction System
The heart's built-in electrical network that coordinates each heartbeat. It includes the sinoatrial (SA) node (the natural pacemaker), the atrioventricular (AV) node, the bundle of His, and the Purkinje fibres.
Think of it as the heart's wiring. The SA node fires an electrical impulse, that impulse travels through a defined pathway, and each chamber contracts in the correct sequence. When the wiring malfunctions, the result is an arrhythmia.
Tags: conduction system, SA node, AV node, bundle of His, Purkinje fibres, cardiac electrical system, heart rhythm
Congenital
Present from birth. A congenital condition is one that exists at or before birth, regardless of whether it was inherited genetically or caused by environmental factors during development.
In simple terms, the person was born with it. "Congenital" says nothing about severity or cause, only timing.
Tags: congenital, born with, present at birth, congenital condition
Congenital Heart Defects
Structural problems with the heart that are present from birth. Examples include holes between heart chambers (septal defects), malformed valves, and abnormal connections between major vessels.
Think of it as: the heart's construction had a fault during development. Some defects are minor and resolve on their own; others require surgical correction in infancy. Common types include atrial septal defect (ASD), ventricular septal defect (VSD), and tetralogy of Fallot.
Tags: congenital heart defects, CHD, septal defect, ASD, VSD, tetralogy of Fallot, heart birth defect
Congestive Heart Failure (CHF)
A chronic condition in which the heart cannot pump blood efficiently enough to meet the body's needs. Blood backs up, causing fluid to accumulate in the lungs (pulmonary congestion), legs, and abdomen.
In simple terms, the pump is weakening. It has not stopped, but it is falling behind. The "congestive" part refers to the fluid buildup that results. CHF can affect the left side (fluid in lungs, shortness of breath), the right side (fluid in legs and abdomen), or both.
Tags: CHF, congestive heart failure, heart failure, pump failure, fluid overload, pulmonary congestion
Cyanosis
A bluish discolouration of the skin, lips, or nail beds caused by low oxygen levels in the blood. It indicates that haemoglobin is carrying insufficient oxygen.
Think of it as: the blood looks blue under the skin because it is not carrying enough oxygen. Central cyanosis (lips, tongue) suggests a systemic oxygenation problem. Peripheral cyanosis (fingers, toes) can also result from poor circulation in cold conditions.
Tags: cyanosis, blue skin, blue lips, low oxygen, deoxygenated haemoglobin, hypoxaemia sign
Cyanotic Heart Disease
A category of congenital heart defects that cause oxygen-poor blood to circulate through the body, resulting in cyanosis. The defect allows deoxygenated blood to bypass the lungs and enter the systemic circulation.
In simple terms, a structural problem in the heart means some blood skips the lungs entirely, so it never picks up oxygen. The classic presentation is a "blue baby" at birth.
Tags: cyanotic heart disease, blue baby, right-to-left shunt, cyanotic congenital heart defect, tetralogy of Fallot
Death Rate (Age-Adjusted)
A statistical measure that accounts for differences in age distribution across populations, allowing fair comparison of mortality rates between groups or over time.
Think of it as: raw death rates can be misleading if one population is much older than another. Age-adjusting removes that bias. When you see "the age-adjusted death rate from heart disease has declined," it means the decline is real and not just an artefact of changing demographics.
Tags: age-adjusted death rate, mortality rate, epidemiology, standardised death rate, population health statistic
Diabetes (Diabetes Mellitus)
A metabolic condition characterised by chronically elevated blood glucose levels. Type 1 results from the immune system destroying insulin-producing cells. Type 2 results from insulin resistance, often linked to obesity and lifestyle.
In simple terms, the body either cannot produce insulin (Type 1) or cannot use it properly (Type 2), so sugar builds up in the blood. Diabetes is a major cardiovascular risk factor because chronic high blood sugar damages blood vessel walls, accelerating atherosclerosis.
Tags: diabetes, diabetes mellitus, Type 1 diabetes, Type 2 diabetes, insulin, blood sugar, hyperglycaemia, cardiovascular risk factor
Diastolic Blood Pressure
The bottom number in a blood pressure reading. It measures the pressure in the arteries when the heart is at rest between beats (during diastole).
Think of it as: the baseline pressure in your pipes when the pump is refilling. A normal diastolic reading is around 80 mmHg. In a reading of 120/80, the 120 is systolic (peak pressure during contraction) and the 80 is diastolic (resting pressure).
Tags: diastolic blood pressure, diastole, bottom number, blood pressure reading, resting arterial pressure
Dissecting Aneurysm
A tear in the inner wall of a large artery (most commonly the aorta) that allows blood to flow between the layers of the vessel wall, splitting them apart. This is a life-threatening emergency.
In simple terms, the artery wall develops a rip, and blood forces its way between the layers like water getting under wallpaper. The vessel can rupture entirely if not treated urgently. Symptoms include sudden, severe "tearing" chest or back pain.
Tags: dissecting aneurysm, aortic dissection, arterial tear, aortic tear, vascular emergency
Edema (Oedema)
Swelling caused by excess fluid trapped in the body's tissues. In the context of cardiovascular disease, oedema typically results from the heart's inability to pump effectively (as in CHF) or from venous insufficiency.
Think of it as: fluid that should be circulating is instead leaking out and pooling. Pitting oedema (where pressing on swollen skin leaves an indent) in the ankles and legs is a classic sign of right-sided heart failure.
Tags: edema, oedema, swelling, fluid retention, pitting oedema, peripheral oedema, heart failure sign
Ejection Fraction (EF)
The percentage of blood that the left ventricle pumps out with each heartbeat. It is one of the most important measures of heart function.
In simple terms, if the ventricle fills with 100 mL of blood and pumps out 65 mL, the ejection fraction is 65%. A normal EF is roughly 55–70%. Below 40% is considered reduced and is a hallmark of systolic heart failure. The formula is: EF = (stroke volume / end-diastolic volume) x 100.
Tags: ejection fraction, EF, left ventricular function, heart pump efficiency, systolic function, stroke volume
The conduction system ensures the heart beats in an organised, rhythmic pattern.
The SA node (right atrium) initiates each heartbeat, earning it the title of the heart's natural pacemaker.
The impulse travels to the AV node (junction of atria and ventricles), then down the bundle of His and into the Purkinje fibres, which trigger ventricular contraction.
Disruptions to this system cause arrhythmias, which can range from benign (occasional extra beats) to fatal (ventricular fibrillation).
Congenital means present from birth. Congenital heart defects are the most common type of birth defect.
Defects are classified as cyanotic (causing low oxygen, blue skin) or acyanotic (no cyanosis).
Cyanotic example: tetralogy of Fallot, a combination of four defects that diverts deoxygenated blood into the systemic circulation.
Acyanotic example: a small atrial septal defect that allows some oxygenated blood to flow back through the lungs unnecessarily, but does not cause cyanosis.
Cyanotic heart disease specifically describes defects that produce a right-to-left shunt, sending oxygen-poor blood to the body. The visible result is cyanosis.
Congestive heart failure is not a sudden event but a progressive decline in the heart's pumping ability.
Left-sided failure: blood backs up into the lungs, causing pulmonary oedema and dyspnoea (shortness of breath).
Right-sided failure: blood backs up into the venous system, causing peripheral oedema (swollen legs) and abdominal swelling (ascites).
Oedema is the physical sign of this fluid backup. It is not a disease itself but a symptom of underlying cardiovascular (or renal) dysfunction.
Ejection fraction quantifies how well the heart is pumping. It is the single most cited number when discussing heart failure severity.
Normal: 55–70%
Mildly reduced: 41–54%
Reduced (systolic heart failure): 40% or below
Diastolic blood pressure represents the lowest arterial pressure during the cardiac cycle. Chronic elevation contributes to vessel damage and increases the risk of stroke and heart attack.
A dissecting aneurysm (aortic dissection) is one of the most dangerous vascular emergencies. The mortality rate increases roughly 1–2% per hour in the first 48 hours without treatment. Key risk factors include chronic hypertension and connective tissue disorders (e.g. Marfan syndrome).
Diabetes mellitus appears in cardiovascular study material because it directly damages blood vessels. Elevated blood glucose promotes atherosclerosis, increases clot risk, and impairs wound healing.
Diabetic patients have roughly two to four times the risk of cardiovascular disease compared to non-diabetic individuals.
Ejection fraction is the number cardiologists use most often to guide treatment decisions in heart failure patients. If a patient's EF drops below 35%, they may become a candidate for an implantable cardioverter-defibrillator (ICD) to prevent sudden cardiac death. Blood pressure measurement, including the diastolic value, is one of the most routine clinical observations worldwide and forms the basis for prescribing antihypertensives.
Students often think "heart failure" means the heart has stopped beating. It has not. The heart is still beating; it is just not pumping efficiently enough. Cardiac arrest (the heart stopping) is a different condition.
Cyanosis is sometimes assumed to mean a patient is not breathing. Cyanosis indicates low blood oxygen, which can result from heart defects, lung disease, or airway obstruction. It is a sign, not a diagnosis.
Students frequently confuse systolic and diastolic pressure. Systolic (top number) is the peak pressure during a heartbeat. Diastolic (bottom number) is the resting pressure between beats.
"Congenital" does not mean "genetic." A congenital condition is present at birth, but it may have been caused by environmental factors during pregnancy (e.g. maternal infections, medications) rather than inherited genes.
⚠️ Ejection fraction values are commonly tested. Know what is normal (55–70%), what constitutes reduced EF (≤40%), and that reduced EF defines systolic heart failure.
⚠️ Be able to distinguish left-sided heart failure symptoms (pulmonary: shortness of breath, crackles in lungs) from right-sided symptoms (systemic: peripheral oedema, jugular vein distension).
⚠️ Know that diabetes is classified as a cardiovascular risk factor. Questions often ask why diabetes appears in a cardiology context.
⚠️ Dissecting aneurysm is a time-critical emergency. Exam questions may present it as sudden, severe, tearing chest/back pain with a history of hypertension.
Q: True or false: The SA node is located in the left atrium.
A: False. It is in the right atrium.
Q: Fill in the blank: A normal ejection fraction is approximately _____ %.
A: 55–70%.
Q: True or false: Congestive heart failure means the heart has completely stopped beating.
A: False. The heart is still beating but is not pumping effectively enough to meet the body's needs.
Q: What does the diastolic number in a blood pressure reading represent?
A: The pressure in the arteries when the heart is at rest between beats.
Q: True or false: All congenital conditions are inherited genetically.
A: False. "Congenital" means present at birth, but the cause may be environmental (e.g. maternal infection during pregnancy) rather than genetic.
Q: A newborn presents with blue-tinged skin shortly after birth. The paediatrician suspects a congenital heart defect. What category of defect is most likely, and what is the underlying mechanism?
A: A cyanotic heart defect. The defect creates a right-to-left shunt, allowing deoxygenated blood to bypass the lungs and enter the systemic circulation, resulting in cyanosis (blue skin).
Q: A patient with CHF has swollen ankles and jugular vein distension. Is this left-sided or right-sided heart failure? Explain.
A: Right-sided heart failure. When the right ventricle cannot pump blood forward into the pulmonary circulation efficiently, blood backs up into the venous system, causing peripheral oedema (swollen ankles) and jugular vein distension.
Q: Why is diabetes mellitus considered a major risk factor for cardiovascular disease?
A: Chronic hyperglycaemia (high blood sugar) damages the walls of blood vessels, accelerates atherosclerosis, increases clotting risk, and impairs wound healing. This makes diabetic patients two to four times more likely to develop cardiovascular disease.
Q: Describe the sequence of electrical conduction through the heart, starting from the SA node.
A: The SA node fires an impulse → the impulse spreads across both atria (causing atrial contraction) → it reaches the AV node, which briefly delays it → the impulse travels down the bundle of His → it splits into the left and right bundle branches → it reaches the Purkinje fibres, which trigger ventricular contraction.
Q: What is a dissecting aneurysm, and why is it a surgical emergency?
A: A tear in the inner wall of a large artery (usually the aorta) that allows blood to force its way between the vessel wall layers. Without treatment, the vessel can rupture completely, causing fatal internal bleeding. Mortality rises roughly 1–2% per hour in the early stages.
The conduction system connects directly to the ECG/EKG unit (covered in Part 3): each wave on an ECG trace corresponds to a specific phase of electrical conduction. Congenital heart defects link to embryology and foetal circulation, particularly the transition at birth when the foramen ovale and ductus arteriosus close. Diabetes ties into endocrinology (insulin, pancreatic function) and renal physiology (diabetic nephropathy).
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