Famous Triads in medicine...

 Charcot's triad for multiple sclerosis

1. Nystagmus
2. Intention tremor
3. Scanning or staccato speech

Charcot's triad for ascending cholangitis

1. Jaundice
2. Fever, usually with rigors
3. Right upper quadrant abdominal pain.

Cushing's triad (not to be confused with the Cushing reflex) is a sign of increased intracranial pressure. It is the triad of:

1. Hypertension (progressively increasing systolic blood pressure)

2. Bradycardia

3. Widening pulse pressure (an increase in the difference between systolic and diastolic pressure over time)

Virchow's triad presents the three broad categories of factors that are thought to contribute to thrombosis.

The triad consists of:

1. Alterations in normal blood flow
2. Injuries to the vascular endothelium
3. Alterations in the constitution of blood (hypercoagulability)

Alteration in blood flow can include turbulence, stasis, mitral stenosis, and varicose veins. Injuries to the vascular endothelium can be cause by damage to the veins arising from shear stress or hypertension.
Hypercoagubility can be a consequence of numerous possible risk factors such as hyperviscosity, deficiency of antithrombin III, nephrotic syndrome, changes after severe trauma or burn, disseminated cancer, late pregnancy and delivery, race, age, smoking, and obesity.

Virchow's triad was first formulated by the German physician Rudolf Virchow (1821-1902) in 1856.

Beck's triad was described by the thoracic surgeon Calude S. Beck in 1935. It's components are:

1. Distended neck veins
2. Distant heart sounds
3. Hypotension

i.e. rising venous pressure, falling arterial pressure, and decreased heart sounds found in the presence of pericardial tamponade.