Cardiac Testing & Imaging

Format: what it is → why it's ordered → what to expect, in plain language. This page covers ECG, ambulatory rhythm monitoring, echo, cardiac MRI, and nuclear imaging — separate from blood tests (see Lab Tests & Diagnostics) and catheter-based procedures and devices (see Procedures & Devices).

Electrocardiogram (ECG or EKG)

A quick, painless recording of your heart's electrical activity using stickers (electrodes) placed on your chest, arms, and legs — takes only a minute or two, no needles, no radiation. It's often the very first cardiac test ordered, since it can reveal a current or prior heart attack, an abnormal rhythm, and structural clues (like chamber enlargement) — though a normal ECG doesn't rule out heart disease, since many conditions don't always show up on a single snapshot.

Preparing for it: none needed — no fasting, no medication changes, and it can be done in a routine office visit.

Holter Monitors & Ambulatory Rhythm Monitoring

A single ECG only captures a snapshot; if your symptoms (palpitations, dizziness, fainting) come and go, your doctor needs a longer recording to catch them in action. Several devices do this, worn at home during normal activity:

• Holter monitor — continuous recording, typically for 24–48 hours, via a small wearable device with electrodes stuck to your chest
• Extended patch monitor (e.g., Zio patch) — a single adhesive patch worn for up to 2 weeks, more comfortable for longer monitoring since there are no wires
• Event monitor — worn for weeks to a month; you (or the device automatically) trigger a recording when symptoms happen, useful for infrequent symptoms a Holter might miss
• Implantable loop recorder — a tiny device placed just under the skin of the chest (a brief outpatient procedure) that continuously monitors for months to years, used when symptoms are too infrequent for even a patch or event monitor to reliably catch

Preparing for it: wear a shirt that's easy to remove for electrode/patch placement; ask about swimming or bathing restrictions, since some patches are water-resistant and others aren't; keep a symptom diary noting the time of anything you feel — correlating your symptoms with what the device recorded is the whole point of the test.

Echocardiogram ("Echo")

An ultrasound of the heart — no radiation, no needles. It measures your ejection fraction, looks at heart valves, chamber sizes, and pressures, and is usually the first major imaging test ordered when heart failure or a structural heart problem is suspected. Most echoes are transthoracic (the probe moves across your chest from outside); occasionally a transesophageal echo (TEE) is needed for a closer look, using a thin probe passed down the esophagus under sedation — typically reserved for specific questions a standard echo can't answer, like examining a valve closely or ruling out a clot before certain procedures.

Preparing for it: a standard (transthoracic) echo needs no special preparation — no fasting, no medication changes. A TEE requires fasting for several hours beforehand (since it involves sedation) and arranging a ride home, since you won't be able to drive afterward.

Cardiac MRI (CMR)

A detailed, non-invasive scan that shows the heart's structure and, importantly, its tissue characteristics — such as scarring from a prior heart attack, inflammation, or infiltration by abnormal proteins (as in amyloidosis). It's often used when echo findings need more detail or a specific cause needs to be identified.

Preparing for it: you'll be screened beforehand for anything metal in your body (certain older pacemakers/ICDs, some implants, metal fragments) since the scanner is a powerful magnet — tell the scheduling team about any implanted device or metal exposure history in advance, not the day of. Contrast (gadolinium) is often used and requires reasonably normal kidney function, checked beforehand. The scan itself takes 30–60 minutes in an enclosed space, worth mentioning to your team in advance if you're prone to claustrophobia — a mild sedative can often be arranged.

Nuclear Cardiac Imaging

Uses a small, safe dose of a radioactive tracer injected into a vein; a special camera then detects where it goes in the heart. Two distinct uses in cardiology:

• Nuclear stress test (myocardial perfusion imaging) — shows blood flow to the heart muscle at rest and after stress (exercise or medication), identifying areas with reduced blood supply from a blocked artery (see Stress Tests, below)
• PYP scan (technetium pyrophosphate scan) — a specialized nuclear scan used specifically to help diagnose one type of cardiac amyloidosis (ATTR) without needing a heart biopsy in many cases — a major advance in how this once under-diagnosed condition is now identified. See Cardiac Amyloidosis

Preparing for it: for a PYP scan, generally no special preparation is needed. For a nuclear stress test, see the stress test preparation guidance below — the imaging portion adds waiting time between the tracer injection and the scan itself, so plan for the appointment to take several hours total.

Cardiac PET (FDG-PET) Scan

A specialized nuclear imaging test that uses a radioactive glucose tracer (FDG, fluorodeoxyglucose) to detect areas of active inflammation in the heart muscle — most notably used to diagnose and monitor cardiac sarcoidosis (see Cardiac Sarcoidosis), and occasionally for certain infections or other inflammatory heart conditions. Unlike a nuclear stress test, which looks at blood flow, a cardiac PET scan looks for metabolically active inflammatory cells.

Why preparation matters so much for this test: your heart muscle normally uses glucose as one of its fuel sources, which would normally light up on an FDG scan and hide the smaller, more specific signal from inflammation. The entire preparation protocol for this test exists to temporarily shift your heart's fuel use away from glucose and toward fat, so that any FDG uptake seen on the scan is more clearly coming from inflammatory cells rather than your heart's normal metabolism.

Preparing for it:

• A high-fat, very low-carbohydrate diet for 24–48 hours before the test — your team will give you a specific list of what to eat and avoid, and following it closely genuinely determines whether the scan is readable
• A prolonged fast immediately before the scan itself (typically starting the night before), per your specific center's protocol
• Avoiding carbohydrates and sugar strictly during the prep window — even small amounts can raise insulin and cause your heart to take up glucose, potentially obscuring the results and requiring the test to be rescheduled
• Some centers use an additional step (like an IV heparin dose before the scan) as part of their specific protocol — your team will explain exactly what your center requires
• Diabetic patients need individualized guidance from their care team on managing blood sugar and medications during the prep period, since the low-carbohydrate requirement intersects directly with diabetes management
• Confirm your specific center's instructions in detail before the day of the test — this is one test where incomplete preparation can mean the scan needs to be repeated entirely

(See Cardiac Sarcoidosis for the condition this test is most often used to evaluate.)

Types of Stress Tests & How to Prepare

"Stress testing" isn't one single test — your doctor chooses the type based on what question needs answering and what you're physically able to do:

General preparation that applies to most stress tests:

• Fasting — typically nothing to eat for 3–4 hours beforehand (exact timing varies by test and site; confirm with your team)
• Medications — you may be asked to hold certain heart medications (especially beta-blockers) the morning of the test, since they can blunt your heart's response and make the test less accurate; never stop a medication on your own — follow your team's specific instructions
• Caffeine — avoid it for 12–24 hours before a pharmacologic stress test using regadenoson or similar medications, since caffeine can interfere with how the medication works
• Clothing and footwear — wear comfortable clothes and walking shoes for an exercise-based test
• Diabetes management — if you take insulin or other diabetes medications, ask your team specifically how to adjust timing around a fasting stress test
• Arrange a ride if your test involves a medication component with sedation-like effects, or if you feel it's needed — otherwise most stress tests don't require someone to drive you home

Common Questions

Related: Lab Tests & Diagnostics · Procedures & Devices · Heart Failure with Reduced Ejection Fraction · Cardiac Amyloidosis · Cardiac Sarcoidosis · Atrial Fibrillation