Isoprenaline, also known as isoproterenol and sold under the brand name Isuprel among others, is a sympathomimetic medication which is used in the treatment of acute bradycardia (slow heart rate), heart block, and rarely for asthma, among other indications. It is used by injection into a vein, muscle, fat, or the heart, by inhalation, and in the past under the tongue or into the rectum.

Side effects of isoprenaline include rapid heart beat, heart palpitations, and arrhythmias, among others. Isoprenaline is a selective agonist of the β-adrenergic receptors, including both the β₁- and β₂-adrenergic receptors. By activating these receptors, it increases heart rate and the force of heart contractions. Chemically, isoprenaline is a synthetic catecholamine and is the N-isopropyl analogue of norepinephrine (noradrenaline) and epinephrine (adrenaline).

Isoprenaline was one of the first synthetic sympathomimetic amines and was the first selective β-adrenergic receptor agonist. The medication was discovered in 1940 and was introduced for medical use in 1947.

Isoprenaline is used to treat heart block and episodes of Adams–Stokes syndrome that are not caused by ventricular tachycardia or fibrillation, in emergencies for cardiac arrest until electric shock can be administered, for bronchospasm occurring during anesthesia, and as an adjunct in the treatment of hypovolemic shock, septic shock, low cardiac output (hypoperfusion) states, congestive heart failure, and cardiogenic shock. It is also used to prevent Torsades de Pointes in patients with long QT refractory to magnesium and to treat patients with intermittent Torsades de Pointes refractory to treatment with magnesium. Isoprenaline is used in the acute management of bradycardia, though not in the chronic treatment of bradycardia.

Historically, it was used to treat asthma via metered aerosol or nebulizing devices; it was also available in sublingual, oral, intravenous, and intramuscular formulations. The U.S. National Asthma Education and Prevention Program Expert Panel recommends against its use as a nebulizer for acute bronchoconstriction.

Many formulations of isoprenaline appear to have been discontinued in the United States and many other countries. In the United States, it remains available only as an injectable solution. It was previously also available in the United States as a solution, metered aerosol, powder, or disc for inhalation and as a tablet for sublingual and rectal administration, but these formulations were discontinued.

It should not be used in people with tachyarrhythmias (except in special circumstances), tachycardia or heart block caused by digitalis poisoning, ventricular arrhythmias which require inotropic therapy, or with angina.

Side effects of isoprenaline may include nervousness, headache, dizziness, nausea, blurred vision, tachycardia, palpitations, angina, Adams-Stokes attacks, pulmonary edema, hypertension, hypotension, ventricular arrhythmias, tachyarrhythmias, difficulty breathing, sweating, mild tremors, weakness, flushing, and pallor. Isoprenaline has been reported to cause insulin resistance leading to diabetic ketoacidosis.