There are a number of different biomarkers used to determine the presence of cardiac muscle damage. Troponins, measured through a blood test, are considered to be the best, and are preferred because they have greater sensitivity and specificity for measuring injury to the heart muscle than other tests. A rise in troponin occurs within 2–3 hours of injury to the heart muscle, and peaks within 1–2 days. The gross value of the troponin, as well as a change over time, are useful in measuring and diagnosing or excluding myocardial infarctions, and the diagnostic accuracy of troponin testing is improving over time. One high-sensitivity cardiac troponin is able to rule out a heart attack as long as the ECG is normal.

Other tests, such as CK-MB or myoglobin, are discouraged. CK-MB is not as specific as troponins for acute myocardial injury, and may be elevated with past cardiac surgery, inflammation or electrical cardioversion; it rises within 4–8 hours and returns to normal within 2–3 days. Copeptin may be useful to rule out MI rapidly when used along with troponin.

Myocardial infarctions are generally clinically classified into ST elevation MI (STEMI) and non-ST elevation MI (NSTEMI). These are based on changes to an ECG. STEMIs make up about 25 – 40% of myocardial infarctions. A more explicit classification system, based on international consensus in 2012, also exists. This classifies myocardial infarctions into five types:

1. Spontaneous MI related to plaque erosion and/or rupture, fissuring, or dissection

2. MI related to ischemia, such as from increased oxygen demand or decreased supply, e.g. coronary artery spasm, coronary embolism, anemia, arrhythmias, high blood pressure or low blood pressure

3. Sudden unexpected cardiac death, including cardiac arrest, where symptoms may suggest MI, an ECG may be taken with suggestive changes, or a blood clot is found in a coronary artery by angiography and/or at autopsy, but where blood samples could not be obtained, or at a time before the appearance of cardiac biomarkers in the blood

4. Associated with coronary angioplasty or stents

- Associated with percutaneous coronary intervention (PCI)

- Associated with stent thrombosis as documented by angiography or at autopsy

5. Associated with CABG

The survival of PVF largely depends on the promptness of defibrillation. The success rate of prompt defibrillation during monitoring is currently higher than 95%. It is estimated that the success rate decreases by 10% for each additional minute of delay.

After return of heart function, there has been a moderately higher risk of death in the hospital when compared to MI patients without PVF. Whether this still holds true with the recent changes in treatment strategies of earlier hospital admission and immediate angioplasty with thrombus removal is unknown. PVF does not affect the long-term prognosis.

There are various risk assessment systems for determining the risk of coronary artery disease, with various emphasis on different variables above. A notable example is Framingham Score, used in the Framingham Heart Study. It is mainly based on age, gender, diabetes, total cholesterol, HDL cholesterol, tobacco smoking and systolic blood pressure.

Ischemic cardiomyopathy can be diagnosed via magnetic resonance imaging (MRI) protocol, imaging both global and regional function. Also the Look-Locker technique is used to identify diffuse fibrosis; it is therefore important to be able to determine the extent of the ischemic scar. Some argue that only left main- or proximal-left anterior descending artery disease is relevant to the diagnostic criteria for ischemic cardiomyopathy. Myocardial imaging usually demonstrates left ventricular dilation, severe ventricular dysfunction, and multiple infarctions. Signs include congestive heart failure, angina edema, weight gain and fainting, among others.

Blood tests routinely performed include electrolytes (sodium, potassium), measures of kidney function, liver function tests, thyroid function tests, a complete blood count, and often C-reactive protein if infection is suspected. An elevated B-type natriuretic peptide (BNP) is a specific test indicative of heart failure. Additionally, BNP can be used to differentiate between causes of dyspnea due to heart failure from other causes of dyspnea. If myocardial infarction is suspected, various cardiac markers may be used.

According to a meta-analysis comparing BNP and N-terminal pro-BNP (NTproBNP) in the diagnosis of heart failure, BNP is a better indicator for heart failure and left ventricular systolic dysfunction. In groups of symptomatic patients, a diagnostic odds ratio of 27 for BNP compares with a sensitivity of 85% and specificity of 84% in detecting heart failure.

In "stable" angina, chest pain with typical features occurring at predictable levels of exertion, various forms of cardiac stress tests may be used to induce both symptoms and detect changes by way of electrocardiography (using an ECG), echocardiography (using ultrasound of the heart) or scintigraphy (using uptake of radionuclide by the heart muscle). If part of the heart seems to receive an insufficient blood supply, coronary angiography may be used to identify stenosis of the coronary arteries and suitability for angioplasty or bypass surgery.

Stable coronary artery disease (SCAD) is also often called stable ischemic heart disease (SIHD). A 2015 monograph explains that "Regardless of the nomenclature, stable angina is the chief manifestation of SIHD or SCAD." There are U.S. and European clinical practice guidelines for SIHD/SCAD.

A complication that may occur in the acute setting soon after a myocardial infarction or in the weeks following is cardiogenic shock. Cardiogenic shock is defined as a hemodynamic state in which the heart cannot produce enough of a cardiac output to supply an adequate amount of oxygenated blood to the tissues of the body.

While the data on performing interventions on individuals with cardiogenic shock is sparse, trial data suggests a long-term mortality benefit in undergoing revascularization if the individual is less than 75 years old and if the onset of the acute myocardial infarction is less than 36 hours and the onset of cardiogenic shock is less than 18 hours. If the patient with cardiogenic shock is not going to be revascularized, aggressive hemodynamic support is warranted, with insertion of an intra-aortic balloon pump if not contraindicated. If diagnostic coronary angiography does not reveal a culprit blockage that is the cause of the cardiogenic shock, the prognosis is poor.

One of the most important features differentiating ischemic cardiomyopathy from the other forms of cardiomyopathy is the shortened, or worsened all-cause mortality in patients with ischemic cardiomyopathy. According to several studies, coronary artery bypass graft surgery has a survival advantage over medical therapy (for ischemic cardiomyopathy) across varied follow-ups.

An electrocardiogram (ECG/EKG) may be used to identify arrhythmias, ischemic heart disease, right and left ventricular hypertrophy, and presence of conduction delay or abnormalities (e.g. left bundle branch block). Although these findings are not specific to the diagnosis of heart failure a normal ECG virtually excludes left ventricular systolic dysfunction.

Unstable angina is characterized by at least one of the following:

1. Occurs at rest or minimal exertion and usually lasts more than 20 minutes (if nitroglycerin is not administered)

2. Being severe (at least Canadian Cardiovascular Society Classification 3) and of new onset (i.e. within 1 month)

3. Occurs with a crescendo pattern (brought on by less activity, more severe, more prolonged or increased frequency than previously).

Fifty percent of people with unstable angina will have evidence of necrosis of the heart's muscular cells based on elevated cardiac serum markers such as creatine kinase isoenzyme (CK)-MB and troponin T or I, and thus have a diagnosis of non-ST elevation myocardial infarction.

When cardiomyopathy is suspected as the cause of cardiogenic shock, a biopsy of heart muscle may be needed to make a definite diagnosis.

Angina should be suspected in people presenting tight, dull, or heavy chest discomfort that is:

1. Retrosternal or left-sided, radiating to the left arm, neck, jaw, or back.

2. Associated with exertion or emotional stress and relieved within several minutes by rest.

3. Precipitated by cold weather or a meal.

Some people present with atypical symptoms, including breathlessness, nausea, or epigastric discomfort or burning. These atypical symptoms are particularly likely in older people, women, and those with diabetes.

Anginal pain is not usually sharp or stabbing or influenced by respiration. Antacids and simple analgesics do not usually relieve the pain. If chest discomfort (of whatever site) is precipitated by exertion, relieved by rest, and relieved by glyceryl trinitrate, the likelihood of angina is increased.

In angina patients momentarily not feeling any chest pain, an electrocardiogram (ECG) is typically normal unless there have been other cardiac problems in the past. During periods of pain, depression, or elevation of the ST segment may be observed. To elicit these changes, an exercise ECG test ("treadmill test") may be performed, during which the patient exercises to his/her maximum ability before fatigue, breathlessness, or pain intervenes; if characteristic ECG changes are documented (typically more than 1 mm of flat or downsloping ST depression), the test is considered diagnostic for angina. Even constant monitoring of the blood pressure and the pulse rate can lead to some conclusion regarding angina. The exercise test is also useful in looking for other markers of myocardial ischemia: blood pressure response (or lack thereof, in particular, a drop in systolic blood pressure), dysrhythmia and chronotropic response. Other alternatives to a standard exercise test include a thallium scintigram or sestamibi scintigram (in patients unable to exercise enough for the purposes of the treadmill tests, e.g., due to asthma or arthritis or in whom the ECG is too abnormal at rest) or Stress Echocardiography.

In patients in whom such noninvasive testing is diagnostic, a coronary angiogram is typically performed to identify the nature of the coronary lesion, and whether this would be a candidate for angioplasty, coronary artery bypass graft (CABG), treatment only with medication, or other treatments. In hospitalized patients with unstable angina (or the newer term of "high-risk acute coronary syndromes"), those with resting ischaemic ECG changes or those with raised cardiac enzymes such as troponin may undergo coronary angiography directly.

The Swan-Ganz catheter or pulmonary artery catheter may assist in the diagnosis by providing information on the hemodynamics.

Hospital admission for people with the following symptoms is recommended, as they may have unstable angina: pain at rest (which may occur at night), pain on minimal exertion, angina that seems to progress rapidly despite increasing medical treatment. All people with suspected angina should be urgently referred to a chest pain evaluation service, for confirmation of the diagnosis and assessment of the severity of coronary heart disease.

Nitroglycerin can be used immediately to widen the coronary arteries and help increase blood flow to the heart. In addition, nitroglycerin causes peripheral venous and artery dilation reducing cardiac preload and afterload. These reductions allow for decreased stress on the heart and therefore lower the oxygen demand of the heart's muscle cells.

Antiplatelet drugs such as aspirin and clopidogrel can help reduce the progression of atherosclerotic plaque formation, as well as combining these with an anticoagulant such as a low molecular weight heparin.

When a stroke has been diagnosed, various other studies may be performed to determine the underlying cause. With the current treatment and diagnosis options available, it is of particular importance to determine whether there is a peripheral source of emboli. Test selection may vary since the cause of stroke varies with age, comorbidity and the clinical presentation. The following are commonly used techniques:

- an ultrasound/doppler study of the carotid arteries (to detect carotid stenosis) or dissection of the precerebral arteries;

- an electrocardiogram (ECG) and echocardiogram (to identify arrhythmias and resultant clots in the heart which may spread to the brain vessels through the bloodstream);

- a Holter monitor study to identify intermittent abnormal heart rhythms;

- an angiogram of the cerebral vasculature (if a bleed is thought to have originated from an aneurysm or arteriovenous malformation);

- blood tests to determine if blood cholesterol is high, if there is an abnormal tendency to bleed, and if some rarer processes such as homocystinuria might be involved.

For hemorrhagic strokes, a CT or MRI scan with intravascular contrast may be able to identify abnormalities in the brain arteries (such as aneurysms) or other sources of bleeding, and structural MRI if this shows no cause. If this too does not identify an underlying reason for the bleeding, invasive cerebral angiography could be performed but this requires access to the bloodstream with an intravascular catheter and can cause further strokes as well as complications at the insertion site and this investigation is therefore reserved for specific situations. If there are symptoms suggesting that the hemorrhage might have occurred as a result of venous thrombosis, CT or MRI venography can be used to examine the cerebral veins.

Nutrition, specifically the Mediterranean-style diet, has the potential for decreasing the risk of having a stroke by more than half. It does not appear that lowering levels of homocysteine with folic acid affects the risk of stroke.

Due to the acute hemodynamic deterioration associated with myocardial rupture, the diagnosis is generally made based on physical examination, changes in the vital signs, and clinical suspicion. The diagnosis can be confirmed with echocardiography. The diagnosis is ultimately made at autopsy.

For acute pericarditis to formally be diagnosed, two or more of the following criteria must be present: chest pain consistent with a diagnosis of acute pericarditis (sharp chest pain worsened by breathing in or a cough), a pericardial friction rub, a pericardial effusion, and changes on electrocardiogram (ECG) consistent with acute pericarditis.

A complete blood count may show an elevated white count and a serum C-reactive protein may be elevated. Acute pericarditis is associated with a modest increase in serum creatine kinase MB (CK-MB). and cardiac troponin I (cTnI), both of which are also markers for injury to the muscular layer of the heart. Therefore, it is imperative to also rule out acute myocardial infarction in the face of these biomarkers. The elevation of these substances may occur when inflammation of the heart's muscular layer in addition to acute pericarditis. Also, ST elevation on EKG (see below) is more common in those patients with a cTnI > 1.5 µg/L. Coronary angiography in those patients should indicate normal vascular perfusion. Troponin levels increase in 35-50% of people with pericarditis.

Electrocardiogram (ECG) changes in acute pericarditis mainly indicates inflammation of the epicardium (the layer directly surrounding the heart), since the fibrous pericardium is electrically inert. For example, in uremia, there is no inflammation in the epicardium, only fibrin deposition, and therefore the EKG in uremic pericarditis will be normal. Typical EKG changes in acute pericarditis includes

- stage 1 -- diffuse, positive, ST elevations with reciprocal ST depression in aVR and V1. Elevation of PR segment in aVR and depression of PR in other leads especially left heart V5, V6 leads indicates atrial injury.

- stage 2 -- normalization of ST and PR deviations

- stage 3 -- diffuse T wave inversions (may not be present in all patients)

- stage 4 -- EKG becomes normal OR T waves may be indefinitely inverted

The two most common clinical conditions where ECG findings may mimic pericarditis are acute myocardial infarction (AMI) and generalized early repolarization. As opposed to pericarditis, AMI usually causes localized convex ST-elevation usually associated with reciprocal ST-depression which may also be frequently accompanied by Q-waves, T-wave inversions (while ST is still elevated unlike pericarditis), arrhythmias and conduction abnormalities. In AMI, PR-depressions are rarely present. Early repolarization usually occurs in young males (age <40 years) and ECG changes are characterized by terminal R-S slurring, temporal stability of ST-deviations and J-height/ T-amplitude ratio in V5 and V6 of <25% as opposed to pericarditis where terminal R-S slurring is very uncommon and J-height/ T-amplitude ratio is ≥ 25%. Very rarely, ECG changes in hypothermia may mimic pericarditis, however differentiation can be helpful by a detailed history and presence of an Osborne wave in hypothermia.

Another important diagnostic electrocardiographic sign in acute pericarditis is the Spodick sign. It signifies to the PR-depressions in a usual (but not always) association with downsloping TP segment in patients with acute pericarditis and is present in up to 80% of the patients affected with acute pericarditis. The sign is often best visualized in lead II and lateral precordial leads. In addition, Spodick’s sign may also serve as an important distinguishing electrocardiographic tool between the acute pericarditis and acute coronary syndrome. The presence of a classical Spodick’s sign is often a giveaway to the diagnosis.

Rarely, electrical alternans may be seen, depending on the size of the effusion.

A chest x-ray is usually normal in acute pericarditis, but can reveal the presence of an enlarged heart if a pericardial effusion is present and is greater than 200 mL in volume. Conversely, patients with unexplained new onset cardiomegaly should always be worked up for acute pericarditis.

An echocardiogram is typically normal in acute pericarditis but can reveal pericardial effusion, the presence of which supports the diagnosis, although its absence does not exclude the diagnosis.

Echocardiography is the main diagnostic tool for LVT. A distinct mass is visible in the left ventricle. Computed Tomography and Magnetic Resonance Imaging are effective, but less common ways to detect LVT, due to their costs and risks. It is possible to assess whether a thrombus will become an embolus through echocardiography. Mobility and protrusion of the thrombus are two characteristics associated with increased embolic potential.

In addition to evaluating the symptoms above, the health care provider may find decreased or no blood pressure in the arm or leg.

Tests to determine any underlying cause for thrombosis or embolism and to confirm presence of the obstruction may include:

- Doppler ultrasound, especially duplex ultrasonography. It may also involve transcranial doppler exam of arteries to the brain

- Echocardiography, sometimes involving more specialized techniques such as Transesophageal echocardiography (TEE) or myocardial contrast echocardiography (MCE) to diagnose myocardial infarction

- Arteriography of the affected extremity or organ Digital subtraction angiography is useful in individuals where administration of radiopaque contrast material must be kept to a minimum.

- Magnetic resonance imaging (MRI)

- Blood tests for measuring elevated enzymes in the blood, including cardiac-specific troponin T and/or troponin I, myoglobins, and creatine kinase isoenzymes. These indicate embolisation to the heart that has caused myocardial infarction. Myoglobins and creatine kinase are also elevated in the blood in embolisation in other locations.

- Blood cultures may be done to identify the organism responsible for any causative infection

- Electrocardiography (ECG) for detecting myocardial infarction

- Angioscopy using a flexible fiberoptic catheter inserted directly into an artery.

The prognosis of myocardial rupture is dependent on a number of factors, including which portion of the myocardium is involved in the rupture. In one case series, if myocardial rupture involved the free wall of the left ventricle, the mortality rate was 100.0%. The chances of survival rise dramatically if the patient: 1. has a witnessed initial event; 2. seeks early medical attention; 3. has an accurate diagnosis by the emergentologist; and 4. happens to be at a facility that has a cardiac surgery service (by whom a quick repair of the rupture can be attempted). Even if the individual survives the initial hemodynamic sequelae of the rupture, the 30‑day mortality is still significantly higher than if rupture did not occur.

The prevalence of LVT with AMI is 5-15%. The rates of AMI associated with LVT is declining due to the use of better therapies and percutaneous coronary intervention used to treat myocardial infarction. LVT formation has been found to be higher in anterior wall AMI than other types of AMI.