Somewhere in your pre-surgery conversations, a number may come up: your STS risk score. It might be described as a 2 percent risk, or 8 percent, or some other figure, and it can land with a thud if no one explains it. The good news is that the STS score is a useful, well-validated tool, and once you understand what it actually measures, it becomes a source of clarity rather than anxiety.
What the STS Score Is
STS stands for the Society of Thoracic Surgeons. The STS Risk Score is a calculator built from the records of millions of real heart surgery patients across the United States. By comparing your characteristics to that enormous database, it estimates the likelihood of specific outcomes for someone like you undergoing a specific operation, such as bypass surgery or valve replacement.
The most commonly cited figure is the Predicted Risk of Mortality, often shortened to PROM, which estimates the chance of not surviving the operation and early recovery. But the score also predicts other outcomes, including stroke, kidney problems, prolonged ventilation, and the chance of a long hospital stay. Together, these give a fuller picture than the single mortality number alone.
How Your Score Is Calculated
The calculator weighs dozens of factors about you and the planned procedure. The major categories include:
- Age and sex
- The specific operation being planned and whether it is elective or urgent
- Heart function, such as your ejection fraction and the severity of valve or artery disease
- Other medical conditions, including diabetes, kidney disease, lung disease, and prior strokes
- Previous heart surgery, which generally raises risk
- General health markers, such as mobility and frailty
Because the score draws on so many variables, two people of the same age can have very different scores. It is genuinely personalized, which is part of why it is trusted.
How to Read Your Number Without Misreading It
Risk categories are often grouped roughly as low (under about 4 percent), intermediate (around 4 to 8 percent), and high (above 8 percent), though the exact thresholds depend on the procedure. A common point of confusion is worth stating plainly: a 3 percent risk of mortality means that, statistically, about 97 of 100 similar patients come through the operation. It describes a population, not a prediction of your individual fate.
The score is also used to guide treatment strategy. For aortic valve disease, for example, the STS score is one of the factors that helps a Heart Team decide between open surgery and a catheter-based approach. If you want a sense of your risk before your appointment, our risk calculator can give you a useful starting estimate to bring into the conversation.
How Your Score Shapes the Treatment Path
Beyond simply estimating risk, the STS score actively guides decisions. The clearest example is aortic valve disease, where teams have historically used risk categories to help sort patients toward open surgery or a catheter-based procedure. A higher score might steer the conversation toward the less invasive option, while a low score in a younger patient might favor surgery for its long-term durability. The score also helps a team decide whether to operate at all in a frail patient, and whether extra precautions or a specialized center are warranted.
It is worth knowing that the score is just one input. A thoughtful Heart Team weighs it alongside your imaging, your symptoms, and your own goals. The number opens the door; it does not walk you through it.
Other Risk Tools You Might Encounter
The STS score is the most widely used calculator in the United States, but you may hear other terms. The EuroSCORE is a similar tool developed in Europe and used in many parts of the world. Some teams also assess frailty separately, using simple measures of strength, walking speed, and independence, because frailty predicts recovery in ways the standard score may underweight. If your team mentions any of these, it is a good sign that they are looking at you as a whole person rather than a single statistic.
You can estimate your own general cardiac risk before your appointment with our risk calculator, which gives you a useful frame of reference to bring into the discussion. For broader background on heart procedures and how they are evaluated, our learn library covers many related topics.
What the STS Score Cannot Tell You
For all its strengths, the score has real limits, and a good team will acknowledge them:
- It does not capture everything. Frailty, nutrition, social support, and certain anatomical details are only partly reflected, yet they meaningfully affect recovery.
- It is an average, not a certainty. No calculator can know which side of the statistics you will land on.
- It does not weigh your goals. Quality of life, your tolerance for risk, and what matters most to you are not in the formula.
- Surgeon and center experience are not in the score. Outcomes vary by program, and a high-volume center may achieve better results than the average the calculator assumes.
This is why the number should open a conversation, not close one.
How to Talk About Your Score With Your Team
If a risk score is part of your evaluation, a few questions help you understand it rather than simply receive it. Asking these tends to produce a richer, more honest conversation:
- What is my predicted risk, and which outcomes does it cover?
- How does my risk compare for the different treatment options being considered?
- Are there factors in my case the score does not fully capture, such as frailty?
- How do this center's actual results compare with the predicted average?
- What can I do before surgery to improve my odds?
That last question matters more than people expect. Some risk is fixed, but some is modifiable. Improving nutrition, gaining strength through gentle activity, optimizing control of diabetes or blood pressure, and stopping smoking can all meaningfully improve how you come through an operation. A score is a snapshot of today, not an unchangeable destiny, and the weeks before a planned procedure are an opportunity to tilt the odds in your favor.
Finally, remember that a score describes risk, not value. A higher number does not mean an operation is not worth doing; for many people, a procedure with meaningful risk is still by far the best path, because the alternative of leaving a serious problem untreated carries its own, often greater, danger. The purpose of the score is to inform the conversation, prepare you and your team, and make sure the decision is taken with eyes open, not to frighten you away from care that could help you live longer and feel better.
Using Your Score in a Second Opinion
An STS score is most powerful when an experienced physician interprets it alongside your full picture. At WhiteGloveMD, a dual-physician Heart Team of a cardiac surgeon and a cardiologist reviews your records, considers your risk score in context, and explains what it means for your specific options. We can tell you whether your risk supports the recommended approach, whether an alternative deserves consideration, and what questions to ask before proceeding. You can learn more about our approach on the cardiac second opinion page or see how it works.
A number on a chart should never be the last word on your heart. WhiteGloveMD gives you a clear, written interpretation from a dual-physician Heart Team, with a 24-hour review after we receive your records and pricing from $500. Request a call to understand what your risk score really means for you.