Cardiovascular Overview

Core Concepts

Anatomy: the pump and its plumbing

Blood flows through the heart in one direction: body → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body. The atrioventricular valves (tricuspid on the right, mitral on the left) separate atria from ventricles; the semilunar valves (pulmonary and aortic) sit at the exits of the ventricles. The heart muscle (myocardium) is thickest in the left ventricle, which must generate enough pressure to push blood through the entire systemic circulation — also why it is most affected by high blood pressure and most commonly involved in heart failure.

The heart receives its own blood supply from the coronary arteries: the left main branches into the left anterior descending (LAD) and circumflex arteries; the right coronary artery supplies the right side of the heart. Notably, the coronary arteries fill during diastole (relaxation), when the aortic valve is closed — which is why a very fast heart rate, which shortens diastole, can reduce the heart's own oxygen supply even while increasing its demand.

The cardiac cycle and heart sounds

One heartbeat is a cardiac cycle with two phases. During diastole, the ventricles relax and fill with blood (most filling is passive, with a final "atrial kick" from atrial contraction). During systole, the ventricles contract, the AV valves close, and blood is ejected into the pulmonary artery and aorta. The familiar "lub-dub" is the sound of the valves closing: S1 ("lub") is closure of the mitral and tricuspid valves at the start of systole; S2 ("dub") is closure of the aortic and pulmonary valves at the end of systole. Extra sounds (S3, S4) and murmurs signal pathology such as volume overload or valvular problems.

Electrical conduction and the ECG

The SA node (in the right atrium) fires about 60–100 times per minute at rest, setting the normal sinus rhythm. The impulse spreads through the atria (producing the P wave on the ECG), pauses at the AV node (the PR interval — a deliberate delay that lets the atria finish emptying before the ventricles contract), travels through the bundle of His and bundle branches, and spreads through the ventricles via the Purkinje fibers (producing the QRS complex). Ventricular recovery produces the T wave. The ECG is a graph of electrical events that predicts mechanical events: a P wave before every QRS at a regular rate tells you the atria and ventricles work in sequence. The next topic (Dysrhythmia) is entirely about what happens when this sequence goes wrong.

Cardiac output, preload, afterload, and contractility

Cardiac output (CO) = heart rate (HR) × stroke volume (SV). Stroke volume is influenced by:

• Preload — the stretch of the ventricular muscle before contraction, determined by how much blood returns to the heart. Within limits, more stretch → stronger contraction (the Frank–Starling law).
• Afterload — the resistance the ventricle must overcome to eject blood. High afterload (as in hypertension) makes ejection harder and increases the heart's workload.
• Contractility — the intrinsic force of the muscle, independent of stretch, enhanced by sympathetic stimulation and reduced by damage (e.g., myocardial infarction).

Blood pressure ≈ cardiac output × systemic vascular resistance. This explains why blood pressure can rise from too much pump output, too much vessel constriction, or both.

The nursing cardiovascular assessment

A focused cardiovascular assessment combines the history (chest pain, dyspnea, palpitations, fatigue, edema, and risk factors) with physical findings: blood pressure, heart rate and rhythm, peripheral pulses, capillary refill, skin color and temperature, edema, and jugular venous distention as a window into right-heart filling pressure. Findings are interpreted in context — dependent edema is common and not always cardiac, so the nurse correlates it with other signs. Diagnostic tools (ECG, echocardiography, cardiac biomarkers) are covered with the specific disorders that use them.

Common Confusions