Heart attacks that occur “out of the blue” may be less common than some people have thought. A major new study suggests that almost everyone who experiences a heart attack, heart failure or stroke for the first time has at least one of four factors that put them at increased risk for these conditions: less than optimal blood pressure, high cholesterol, high blood sugar or being a current or former smoker.

The studiopublished September 29, 2025, i Journal of the American College of Cardiologyincluded more than nine million adults in Korea and nearly 7,000 in the United States. All had repeated health examinations and were followed for up to two decades. More than 99% of people who developed new coronary artery disease, heart failure or stroke had at least one of the risk factors before their diagnosis. High blood pressure was the most common, affecting more than 95% of Koreans and 93% of Americans with new diagnoses.

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