The International Studies of Infarct Survival (ISIS) were four randomized controlled trial

Randomized controlled trial

A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...

s of several drug

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

s for treating suspected acute

Acute (medicine)

In medicine, an acute disease is a disease with either or both of:# a rapid onset, as in acute infection# a short course ....

 myocardial infarction

Myocardial infarction

Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

 ("heart attack"). More than 134,000 patients from over 20 countries took part in four large simple trials between 1981 and 1993, coordinated from Oxford

Oxford

The city of Oxford is the county town of Oxfordshire, England. The city, made prominent by its medieval university, has a population of just under 165,000, with 153,900 living within the district boundary. It lies about 50 miles north-west of London. The rivers Cherwell and Thames run through...

, England.

ISIS-1

The First International Study of Infarct Survival (ISIS-1) was a placebo-controlled trial of the beta-blocker atenolol. It recruited 16,027 patients and was completed in 1985.

ISIS-2

The Second International Study of Infarct Survival (ISIS-2) was a 2×2 factorial

Factorial experiment

In statistics, a full factorial experiment is an experiment whose design consists of two or more factors, each with discrete possible values or "levels", and whose experimental units take on all possible combinations of these levels across all such factors. A full factorial design may also be...

 placebo-controlled trial of aspirin

Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...

 and the thrombolytic drug streptokinase

Streptokinase

Streptokinase , a protein secreted by several species of streptococci can bind and activate human plasminogen. SK is used as an effective and inexpensive thrombolysis medication in some cases of myocardial infarction and pulmonary embolism...

. It recruited 17,187 patients and was completed in 1988.

ISIS-3

The Third International Study of Infarct Survival (ISIS-3) was a 3×2 factorial

Factorial experiment

In statistics, a full factorial experiment is an experiment whose design consists of two or more factors, each with discrete possible values or "levels", and whose experimental units take on all possible combinations of these levels across all such factors. A full factorial design may also be...

 trial that compared the three thrombolytic drugs streptokinase

Streptokinase

Streptokinase , a protein secreted by several species of streptococci can bind and activate human plasminogen. SK is used as an effective and inexpensive thrombolysis medication in some cases of myocardial infarction and pulmonary embolism...

, tissue plasminogen activator

Tissue plasminogen activator

Tissue plasminogen activator is a protein involved in the breakdown of blood clots. It is a serine protease found on endothelial cells, the cells that line the blood vessels. As an enzyme, it catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for clot breakdown...

 (tPA) and anistreplase

Anistreplase

Anistreplase is a thrombolytic drug.Anistreplase has been developed by Beecham as Eminase. It is also known as anisoylated plasminogen streptokinase activator complex -Mechanism:...

 to each other, and also compared the anticoagulant

Anticoagulant

An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

 heparin

Heparin

Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

 to no heparin. All patients were also given aspirin

Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...

. It recruited 41,299 patients and was completed in 1991.

ISIS-4

The Fourth International Study of Infarct Survival (ISIS-4) was a 2×2×2 factorial

Factorial experiment

In statistics, a full factorial experiment is an experiment whose design consists of two or more factors, each with discrete possible values or "levels", and whose experimental units take on all possible combinations of these levels across all such factors. A full factorial design may also be...

 placebo-controlled trial of the angiotensin-converting enzyme

Angiotensin-converting enzyme

Angiotensin I-converting enzyme , an exopeptidase, is a circulating enzyme that participates in the body's renin-angiotensin system , which mediates extracellular volume , and arterial vasoconstriction...

 inhibitor (ACE inhibitor

ACE inhibitor

ACE inhibitors or angiotensin-converting enzyme inhibitors are a group of drugs used primarily for the treatment of hypertension and congestive heart failure...

) captopril

Captopril

Captopril is an angiotensin-converting enzyme inhibitor used for the treatment of hypertension and some types of congestive heart failure. Captopril was the first ACE inhibitor developed and was considered a breakthrough both because of its novel mechanism of action and also because of the...

, isosorbide mononitrate and magnesium sulphate. It recruited 58,050 patients and was completed in 1993.