Introduction
Heart surgery helps many people, but every operation carries some risk. This STS Risk Calculator gives you a quick estimate of that risk before surgery. You type in details about the patient and the planned operation, and the tool shows the chance of death and of other serious problems.
The calculator asks about the type of heart surgery, how urgent it is, age, sex, height, weight, ejection fraction, and health problems like diabetes, kidney disease, lung disease, and past heart surgery. It then shows estimates for:
- Operative mortality (death from the surgery)
- Major problems or death (composite risk)
- Long time on a breathing machine
- Stroke
- Kidney failure
- Deep chest wound infection
- Needing a second operation
- A long hospital stay
Each result gets a low, intermediate, or high risk label. You also get a plain-language patient summary, a list of the factors that push risk up the most, and a "what-if" tool that shows how the numbers change if things like kidney function or heart pumping improve. Every step of the math is shown, so you can see where the number comes from.
Important: This tool is for learning only. It uses a simplified model and does not match the official Society of Thoracic Surgeons risk score. Do not use it to make care decisions. Always use the official STS Online Risk Calculator and talk with the heart surgery team.
How to use our STS Risk Calculator
Enter the planned heart surgery, the patient's basic details, heart history, and other health problems. The calculator then shows the predicted risk of death, stroke, kidney failure, wound infection, long ventilator time, reoperation, long hospital stay, and a combined major risk score, plus a clinical summary and step-by-step math.
Procedure Type: Pick the operation planned, such as CABG only, isolated valve, or CABG plus valve. Fields that do not fit are turned off.
Valve Position: If a valve is being fixed or replaced, choose aortic, mitral, tricuspid, or pulmonic.
Surgical Urgency: Choose elective, urgent, emergent, or emergent salvage based on how fast surgery must happen.
Diseased Coronary Vessels: Select how many coronary arteries are blocked, from 0 to 3.
Left Main Stenosis ≥ 50%: Turn this on if the left main artery is narrowed by half or more.
Age: Type the patient's age in years, from 18 to 110.
Biological Sex: Choose male or female.
Race / Ethnicity: Pick the group that best fits the patient.
Height: Enter height and pick your unit: cm, m, inches, or feet.
Weight: Enter weight and pick kg, lb, or stone.
Body Mass Index: This box fills in by itself from height and weight. You do not type anything here.
Ejection Fraction: Use the slider or type the pumping strength of the heart, from 0% to 80%.
Prior Cardiac Surgery: Choose none, one past heart operation, or two or more.
Prior PCI: Turn this on if the patient had a stent or balloon procedure before.
Prior Myocardial Infarction: Turn this on if the patient has had a heart attack.
MI Timing: If there was a heart attack, say if it was within 21 days or longer ago.
Congestive Heart Failure: Turn this on if the patient has heart failure.
NYHA Class: If heart failure is on, pick class I to IV for how bad the symptoms are.
Unstable Angina: Turn this on for chest pain at rest or getting worse.
Cardiogenic Shock: Turn this on if the heart cannot pump enough blood to the body.
Intra-Aortic Balloon Pump: Turn this on if a balloon pump is in place.
IV Inotropes: Turn this on if drugs are being given through a vein to help the heart pump.
Resuscitation < 1 h Pre-op: Turn this on if CPR was needed within one hour before surgery.
Diabetes Mellitus: Choose none, diet-controlled, oral agent, or insulin.
COPD: Choose none, mild, moderate, or severe lung disease.
Serum Creatinine: Enter the blood test value in mg/dL or µmol/L. This box turns off if dialysis is selected.
Dialysis-Dependent: Turn this on if the patient is on dialysis.
Hypertension: Turn this on for high blood pressure.
Dyslipidemia: Turn this on for high cholesterol or fats in the blood.
Peripheral Arterial Disease: Turn this on if leg or arm arteries are narrowed.
Cerebrovascular Disease: Turn this on for past stroke or brain artery disease.
Carotid Artery Disease: Turn this on if the neck arteries are narrowed.
Immunocompromised: Turn this on for a weak immune system, such as from steroids or cancer drugs.
Active Endocarditis: Turn this on if there is a current heart valve infection.
Liver Disease: Turn this on for cirrhosis or other liver problems.
What-If Fields: Change the ejection fraction, creatinine, diabetes control, or urgency to see how the risk would change. Click "Match current inputs" to copy the real values back in.
Click Calculate to update the results, Reset to start over, or Print Summary to save a copy. These numbers are for learning only and are not the official STS risk score.
What Is the STS Risk Score?
The STS risk score is a tool that heart doctors use to guess how risky heart surgery may be for one patient. STS stands for the Society of Thoracic Surgeons. The group collects data from thousands of real heart operations in a large database. That data is used to build a math model that predicts the chance of death or serious problems after surgery.
Why Heart Surgery Risk Is Measured
Two people can need the same operation but face very different risks. A healthy 55-year-old is not the same as an 80-year-old with weak kidneys and a weak heart pump. Doctors need numbers, not just a feeling, so they can plan care and talk clearly with patients and families.
The best known number is the Predicted Risk of Mortality (PROM). It is the chance a patient dies in the hospital or within 30 days of surgery. Heart teams often sort patients into groups:
- Low risk: under 4%
- Intermediate risk: 4% to 8%
- High risk: over 8%
Outcomes the Model Looks At
Death is not the only thing that matters. The STS model also predicts other bad outcomes after heart surgery:
- Prolonged ventilation: needing a breathing machine for more than 24 hours.
- Stroke: lasting brain damage.
- Renal failure: new dialysis or a big jump in creatinine.
- Deep sternal wound infection: a deep chest bone infection.
- Reoperation: going back to the operating room.
- Prolonged length of stay: more than 14 days in the hospital.
- Major morbidity or mortality: a combined score of any of the above plus death.
What Raises Surgical Risk
Many things push risk up. The biggest ones are usually:
- Age. Risk climbs steadily after about 65.
- Urgency. An elective case is much safer than an emergency or salvage case.
- Type of operation. CABG alone is safer than CABG plus a valve, double valve, or aortic root work.
- Heart pump strength. A low ejection fraction means a weaker heart.
- Kidney health. High creatinine or dialysis raises risk a lot.
- Shock, balloon pump, or IV drugs. These show the heart is failing right now.
- Past heart surgery. Redo chests are harder and bleed more.
- Lung disease, diabetes, liver disease, and blood vessel disease.
How Risk Models Work
These models use logistic regression. Each risk factor gets a weight, called a coefficient. The weights are added up into one number, the log-odds. That number is then turned into a percent between 0 and 100. So a patient's final risk is really just the sum of many small pushes up or down.
How Doctors Use the Score
Heart teams use STS scores to choose between open surgery and less invasive options. A common example is aortic valve disease. High STS scores often point toward TAVR (a valve placed through a catheter) instead of open surgery. Hospitals also use these scores to check their own results, since a program with sicker patients should be judged against expected risk, not raw numbers.
Important Limits
A risk score is an estimate for a group of similar patients, not a promise for one person. It cannot measure frailty, surgeon skill, hospital volume, or a patient's own goals. Only the official STS Online Risk Calculator gives true STS values. Any score should be discussed with a cardiac surgeon and cardiologist before making a decision, alongside longer-term measures such as the 10-year chance of a heart attack or stroke.