Angina pectoris is not a disease in isolation: it is the clinical expression of myocardial ischemia, arising whenever oxygen demand exceeds the capacity of the coronary circulation to deliver oxygenated blood.1 Understanding angina pharmacologically begins not with individual drugs but with a clear map of the hemodynamic determinants of myocardial oxygen consumption (MVO2) and the mechanisms by which the coronary vasculature fails to meet demand.2·12 Every antianginal drug class acts on one or more of these determinants; rational prescribing requires knowing precisely which levers are being pulled, and in which direction.2·3
This module establishes that conceptual foundation: the supply-demand framework, the classification of angina subtypes, the hemodynamic targets available to pharmacological intervention, and the rationale for combination therapy.
The myocardium is an obligate aerobe with a near-maximal baseline oxygen extraction ratio (~70-75% at rest, compared to ~25% in skeletal muscle).12 Unlike skeletal muscle, the heart cannot significantly increase oxygen extraction in response to increased demand; it must increase coronary blood flow. This fundamental limitation means that any condition reducing coronary flow or increasing demand risks ischemia.12
The major determinants of MVO2 are as follows. Heart rate is the single most important determinant of MVO2.12 Each cardiac cycle consumes energy; doubling HR nearly doubles oxygen consumption. Increased HR also shortens diastole disproportionately, since coronary perfusion occurs predominantly during diastole (left ventricle), and tachycardia simultaneously increases demand and reduces supply. The rate-pressure product (HR x systolic BP) provides a practical clinical correlate of MVO2 and reliably predicts the anginal threshold in stable disease.2·5 Ventricular wall stress is described by the Law of Laplace: Wall Stress = (Pressure x Radius) / (2 x Wall Thickness).12 Elevated filling pressures (preload) increase end-diastolic radius, raising wall stress. Elevated systemic vascular resistance (afterload) increases systolic pressure, further raising wall stress. Ventricular hypertrophy increases wall thickness and reduces wall stress, a compensatory but ultimately maladaptive response. Contractility is a third major demand determinant: greater force of contraction requires more cross-bridge cycling and more ATP hydrolysis.12 Catecholamine excess (exercise, emotional stress, cocaine use) drives both HR and contractility simultaneously. Clinically, contractility is the hardest determinant to modulate without hemodynamic compromise. Myocardial wall mass is the fourth determinant: hypertrophied ventricles have increased MVO2 at baseline, and subendocardial ischemia is more common in left ventricular hypertrophy (LVH) because subendocardial vessels are more susceptible to compressive forces and operate at lower perfusion pressures.12
Ranked by pharmacological accessibility: heart rate is highly modifiable (beta-blockers, CCBs, ivabradine); preload and wall stress are modifiable (nitrates, diuretics); afterload is modifiable (nitrates, CCBs, ACE inhibitors); contractility is modifiable (beta-blockers, non-dihydropyridine CCBs); wall mass is not acutely modifiable.
Coronary oxygen supply is determined by: Supply = Coronary Blood Flow x Arterial Oxygen Content.12 Coronary blood flow (CBF) depends on coronary perfusion pressure (aortic diastolic pressure minus left ventricular end-diastolic pressure (LVEDP)), coronary vascular resistance (determined by fixed stenoses, dynamic vasomotion, autoregulatory reserve, and extravascular compressive forces),12 and heart rate via diastolic time. Arterial oxygen content is determined by hemoglobin concentration and saturation; this is relevant in anemia- or hypoxia-triggered angina but is not a direct target of antianginal pharmacotherapy.
THE ISCHEMIC CASCADE: When supply falls below demand, the sequence is as follows.12 First, metabolic changes (lactate production, ATP depletion) occur. Second, diastolic dysfunction (impaired relaxation) develops. Third, systolic dysfunction (regional wall motion abnormality) appears. Fourth, ECG changes (ST depression or elevation) emerge. Fifth and last, anginal symptoms appear. This sequence has important implications: ischemia is already physiologically significant before the patient reports symptoms. Symptom-guided therapy alone may underestimate the burden of ischemia.6
Fixed atherosclerotic stenosis limits the capacity to increase coronary blood flow in response to demand.2·12 At rest, residual flow through the stenosis (and collaterals) is adequate. With exertion or emotional stress (when HR, contractility, and wall stress all increase), the fixed supply cannot match escalating demand. Key features include a predictable threshold at a reproducible rate-pressure product;2·5 relief by rest within 2-5 minutes or by sublingual NTG within 1-3 minutes;2 a pathological substrate of stable fibrofatty plaque with intact fibrous cap, typically >70% luminal stenosis;12 and endothelial dysfunction with documented paradoxical vasoconstriction at stenosis sites during exercise.12
CANADIAN CARDIOVASCULAR SOCIETY (CCS) CLASSIFICATION:11 Class I: angina only with strenuous exertion; ordinary activity unrestricted. Class II: slight limitation; angina with brisk walking upstairs, hills, or after meals. Class III: marked limitation; angina with 1-2 level blocks on flat ground. Class IV: inability to perform any activity without symptoms; possible angina at rest. The CCS class guides both pharmacological intensity and the threshold for revascularization referral.2·3
Focal or diffuse epicardial coronary artery spasm produces transient, severe reduction in coronary blood flow, which is a pure supply-side failure.7 Unlike stable angina, MVO2 is normal; ischemia results entirely from reduced perfusion. Mechanism of spasm involves hyperreactivity of coronary smooth muscle to vasoconstrictors (endothelin-1, serotonin, histamine, alpha-adrenergic stimulation); reduced endothelial nitric oxide bioavailability; and may occur on angiographically normal coronary arteries or at sites of non-obstructive plaque.7·8 Triggers include cold exposure, hyperventilation, cocaine, triptans, ergot alkaloids, and emotional stress.8
Clinical features include episodes predominantly at rest, classically in the early morning hours (circadian pattern of increased sympathetic tone and reduced NO); transient ST elevation (transmural ischemia) rather than ST depression; rapid relief with sublingual NTG; and preserved or near-normal epicardial coronary arteries on angiography.7·8 Diagnosis is confirmed by acetylcholine or ergonovine provocation testing. Management centers on calcium channel blockers (first-line) and long-acting nitrates. Beta-blockers are contraindicated: beta-2 blockade removes coronary vasodilatory tone, leaving unopposed alpha-1-mediated vasoconstriction.7·8
Microvascular angina (MVA) results from dysfunction of the coronary microvasculature (vessels <500 microns in diameter), which are the resistance vessels responsible for autoregulation of coronary blood flow.9 Epicardial coronary arteries are angiographically normal or near-normal. The fundamental abnormality is impaired coronary flow reserve (CFR): the microvasculature cannot adequately dilate in response to increased demand, producing subendocardial ischemia.9 Mechanisms include endothelial dysfunction with reduced NO bioavailability, smooth muscle hyperreactivity, perivascular fibrosis, and autonomic dysregulation. MVA is particularly prevalent in post-menopausal women, patients with hypertension, diabetes, and LVH.9
Clinical features include typical anginal symptoms (often more prolonged than stable exertional angina); positive stress test; normal epicardial coronary arteries; and CFR <2.0 on functional testing (positron emission tomography (PET), cardiac magnetic resonance (CMR), or intracoronary wire).9 Sublingual nitroglycerin (SL-NTG) may be less effective or paradoxically worsen symptoms (possible microvascular steal). Management includes beta-blockers, CCBs, ACE inhibitors, and ranolazine.9
Unstable angina (UA) and non-ST-elevation MI (NSTEMI) represent acute coronary syndromes characterized by plaque rupture or erosion with superimposed thrombosis, producing a dynamic and potentially total coronary occlusion.10 The pathophysiology differs from stable angina: the ischemia is demand-independent, arising from acute reduction in supply. Antianginal drugs are used acutely in ACS for hemodynamic stabilization and symptom control, not as primary anti-ischemic therapy. Revascularization and antithrombotic therapy are the cornerstones of ACS management.10
The hemodynamic rationale for antianginal use in the acute ACS setting is demand reduction while awaiting definitive treatment. Intravenous nitroglycerin is indicated for persistent ischemic symptoms, hypertensive emergency with ACS, or pulmonary congestion (ACC/AHA Class I).10 Its primary mechanism in this context is preload reduction: rapid venodilation reduces LVEDP, decreasing subendocardial compressive forces and improving perfusion to the ischemic zone. At higher infusion rates (greater than 100 mcg/min), progressive arterial dilation reduces afterload and increases cardiac output, which is particularly beneficial in acute decompensated heart failure complicating ACS.10 Beta-blockers reduce HR and contractility, blunting the sympathetically driven demand surge that accompanies the pain and anxiety of ACS. Oral beta-blockade within the first 24 hours of NSTEMI is recommended when there is no evidence of acute heart failure, low-output state, or significant bradycardia (ACC/AHA Class I); intravenous beta-blocker is reserved for ongoing hypertension or tachyarrhythmia uncontrolled by oral dosing.10
Two critical contraindications in the ACS setting must be understood. First, nitrates are absolutely contraindicated within 24 to 48 hours of phosphodiesterase-5 inhibitor use (sildenafil, vardenafil, tadalafil) due to the risk of catastrophic hypotension from potentiated cGMP accumulation in vascular smooth muscle.10 Before administering any nitrate in the acute setting, phosphodiesterase-5 inhibitor use must be confirmed as absent. Second, nitrates are contraindicated in right ventricular infarction. Right ventricular function in the setting of inferior ST-elevation myocardial infarction (STEMI) with right ventricular involvement depends on preload; the failing right ventricle requires high filling pressures to maintain forward output across the pulmonary circulation. Nitrate-induced venodilation reduces venous return and right ventricular preload, precipitating severe hypotension and hemodynamic collapse.10 Right ventricular infarction should be excluded by right-sided electrocardiogram leads (ST elevation in V4R) before nitrates are administered in any inferior ST-elevation myocardial infarction. In confirmed right ventricular infarction, the treatment of hypotension is volume loading, not vasodilation.
The rate-pressure product (RPP = HR x systolic BP) is the most clinically useful bedside surrogate for MVO2 and reliably predicts the anginal threshold in individual patients.2·5 A patient with stable angina reaches their ischemic threshold at a reproducible RPP, for example 26,000 mmHg/min. Effective antianginal therapy shifts the RPP demand curve downward so that ordinary daily activities no longer reach the ischemic threshold. The therapeutic target is a resting HR of 55-60 bpm and a resting RPP reduced by at least 15-20% from pre-treatment baseline.2·3
PRELOAD REDUCTION: reduces LVEDP and ventricular end-diastolic volume → decreases wall stress and subendocardial compressive forces → improves subendocardial perfusion and reduces MVO2. Agents: organic nitrates (venodilation via NO-cGMP pathway). Most effective at standard doses; large capacitance veins are the primary target.4
AFTERLOAD REDUCTION: reduces systolic wall stress → reduces MVO2. Also increases stroke volume at any given preload. Agents: dihydropyridine CCBs (amlodipine, nifedipine), nitrates at higher doses, ACE inhibitors/ARBs. Primary mechanism of DHP-CCBs in angina.3
HEART RATE REDUCTION: the most powerful single anti-ischemic lever. Reduces MVO2 (fewer cycles per minute) and simultaneously prolongs diastole → increases coronary filling time. Agents: beta-blockers (SA node beta-1 blockade), non-DHP CCBs (diltiazem, verapamil, via direct SA node Ca2+ channel blockade), ivabradine (selective If channel inhibition in SA node).2·3
CORONARY VASODILATION: increases coronary oxygen supply. Agents: nitrates (epicardial coronary dilation, predominantly; limited microvascular effect), DHP-CCBs (coronary smooth muscle relaxation, particularly effective in vasospasm), non-DHP CCBs (coronary vasodilation with rate reduction). All CCBs block L-type Ca2+ channels in coronary smooth muscle.3
No single drug class addresses all four hemodynamic levers simultaneously, and each class has dose-limiting adverse effects that prevent indefinite escalation. Combination therapy exploits pharmacological complementarity: adding agents with different mechanisms achieves greater total MVO2 reduction at lower doses of each individual drug, thereby improving efficacy while limiting adverse effects.2·3 The preferred first combination is beta-blocker + dihydropyridine calcium channel blocker (DHP-CCB) (amlodipine): the beta-blocker contributes HR and contractility reduction and blocks the reflex tachycardia triggered by the DHP-CCB's vasodilation; the DHP-CCB contributes afterload reduction and coronary vasodilation without additive AV conduction depression.2·3 The addition of a long-acting nitrate (preload reduction) completes triple conventional therapy for CCS III-IV patients. Non-hemodynamic agents (ranolazine, ivabradine) can be added when hemodynamic targets have been reached but symptoms persist.2·3
Because vasospastic angina is a pure supply-side disorder (MVO2 is normal), demand-reduction strategies are physiologically irrelevant as primary therapy.7·8 CCBs are the first-line treatment because they directly inhibit the pathological Ca2+-mediated smooth muscle hyperreactivity responsible for spasm. Beta-blockers are contraindicated: by blocking beta-2 receptors (which normally mediate coronary vasodilation), beta-blockers leave alpha-1-mediated vasoconstriction unopposed, potentially precipitating or worsening spasm.7·8 This is a class effect: it applies to all beta-blockers including cardioselective agents.
In MVA, the ischemia arises from the inability of the microvasculature to augment flow, a process not reliably modulated by any single drug class.9 Nitrates may paradoxically worsen symptoms in some patients (microvascular steal). CCBs and beta-blockers provide partial benefit in approximately 40-50% of patients. Ranolazine (late INa inhibition → improved diastolic function → reduced LVEDP → improved subendocardial perfusion) has emerging evidence in MVA. ACE inhibitors improve endothelial NO bioavailability and microvascular function.9 Management often requires combination of multiple agents with modest individual effects.
The supply-demand framework is the conceptual backbone of all antianginal pharmacotherapy. Myocardial ischemia occurs when oxygen demand (determined by HR, wall stress, and contractility) exceeds oxygen supply (determined by coronary perfusion pressure, vascular resistance, and diastolic filling time).12 Every antianginal drug class reduces ischemia by modifying one or more of these determinants, a principle that both explains why individual agents work and guides rational combination therapy. The distinction between stable exertional angina (fixed supply deficit, demand-driven ischemia), vasospastic angina (dynamic supply failure, normal demand), and microvascular angina (microvascular flow reserve impairment) determines which pharmacological levers are appropriate and which are contraindicated for each individual patient.2·3·7·8·9
Libby P, Bonow RO, Mann DL, et al. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia: Elsevier; 2022. Chapter 38: Stable Ischemic Heart Disease.
Knuuti J, Wijns W, Saraste A, et al. 2019 ESC Guidelines for the diagnosis and management of chronic coronary syndromes. Eur Heart J. 2020;41(3):407-477
doi:10.1093/eurheartj/ehz425Fihn SD, Gardin JM, Abrams J, et al. 2012 ACCF/AHA Guideline for the diagnosis and management of patients with stable ischemic heart disease. J Am Coll Cardiol. 2012;60(24):e44-e164
doi:10.1016/j.jacc.2012.07.013Parker JD, Parker JO. Nitrate therapy for stable angina pectoris. N Engl J Med. 1998;338(8):520-531
doi:10.1056/NEJM199802193380807Deedwania PC, Carbajal EV. Role of myocardial oxygen demand in the pathophysiology of silent myocardial ischemia. Am J Cardiol. 1992;70(9):19F-24F
doi:10.1016/0002-9149(92)90185-2Cohn PF. Silent myocardial ischemia. Ann Intern Med. 1988;109(4):312-317
doi:10.7326/0003-4819-109-4-312Beltrame JF, Crea F, Kaski JC, et al. International standardization of diagnostic criteria for vasospastic angina. Eur Heart J. 2017;38(33):2565-2568
doi:10.1093/eurheartj/ehv351Yasue H, Nakagawa H, Itoh T, et al. Coronary artery spasm — clinical features, diagnosis, pathogenesis, and treatment. J Cardiol. 2008;51(1):2-17
doi:10.1016/j.jjcc.2008.01.001Crea F, Bairey Merz CN, Beltrame JF, et al. The parallel tales of microvascular angina and heart failure with preserved ejection fraction. Eur Heart J. 2017;38(7):473-477
doi:10.1093/eurheartj/ehw461Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC Guideline for the management of patients with non-ST-elevation acute coronary syndromes. J Am Coll Cardiol. 2014;64(24):e139-e228
doi:10.1016/j.jacc.2014.09.017Campeau L. The Canadian Cardiovascular Society grading of angina pectoris revisited 30 years later. Can J Cardiol. 2002;18(4):371-379. PMID: 11950273
Opie LH. Heart Physiology: From Cell to Circulation. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2004. Chapter 11: Oxygen Consumption and the Supply-Demand Ratio.