For many people, a diagnosis of heart disease comes as a complete surprise. But for a growing number of individuals, that cardiac event is the first clue that something else has been going on quietly for years: type 2 diabetes. The relationship between these two conditions is so tightly linked that heart disease is now considered an early red flag for undiagnosed diabetes in some people.
If you or a loved one has recently been diagnosed with coronary artery disease, a heart attack, or heart failure, understanding the connection to blood sugar control is critical. Here’s what the latest research reveals about why your heart might sound the alarm before your glucose levels ever get checked.
Why the heart is often the first to notice
Type 2 diabetes does not appear overnight. Before a formal diagnosis, many people spend years in a state of insulin resistance or prediabetes, where blood sugar levels are higher than normal but not yet in the diabetic range. During this period, elevated insulin and glucose are quietly damaging blood vessels throughout the body.
The heart and its arterial network are especially vulnerable. Endothelial cells that line the arteries become inflamed and less flexible. Small plaques begin to form. Over time, these changes can restrict blood flow or trigger a sudden blockage. For many people, the first symptom they feel is chest pain or a heart attack—not the classic diabetes signs like excessive thirst or frequent urination.
What the research shows
Large epidemiological studies have consistently found that people with undiagnosed diabetes have a significantly higher risk of cardiovascular events. One landmark analysis published in Circulation estimated that roughly 10–15% of patients presenting with a first heart attack have undiagnosed diabetes. Even more striking, about one-third of people hospitalized for acute coronary syndrome have prediabetes that was previously unrecognized.
The mechanism is straightforward: elevated blood sugar accelerates atherosclerosis. It promotes oxidative stress, glycation of proteins, and dysfunction of the blood vessel lining. When you combine these factors with the hypertension and abnormal cholesterol that often accompany insulin resistance, the cardiovascular system takes a heavy hit long before blood sugar crosses the diagnostic threshold.
Who is most at risk?
Not everyone with heart disease has undiagnosed diabetes, but certain factors increase the likelihood. Those who are overweight or obese, have a family history of diabetes, lead a sedentary lifestyle, or have a history of gestational diabetes are at higher risk. Ethnicity also plays a role—people of South Asian, African, Hispanic, and Indigenous descent have a greater predisposition to insulin resistance and diabetes.
Age is another factor. Adults over 45 should be especially vigilant, though younger individuals with heart disease and metabolic risk factors should also be screened. If you have ever been told you have borderline high blood sugar or prediabetes, and you later develop heart disease, the connection is especially relevant.
How doctors screen for diabetes after a heart event
If you are hospitalized for a heart attack, angina, or heart failure, standard protocol now includes a blood sugar check. But a single glucose reading can be misleading—stress from the cardiac event itself can temporarily raise blood sugar, a phenomenon known as stress hyperglycemia.
To get an accurate picture, physicians typically order a fasting plasma glucose test and a hemoglobin A1c, which reflects average blood sugar over the past two to three months. An A1c of 6.5% or higher confirms diabetes; 5.7–6.4% indicates prediabetes. An oral glucose tolerance test may also be used if results are borderline.
The American Diabetes Association now recommends that anyone with established cardiovascular disease be screened for diabetes, even if they have no symptoms. This is not an optional check—it is considered standard of care.
What a dual diagnosis means for treatment
When heart disease and diabetes are found together, treatment plans change. Blood pressure and cholesterol targets become stricter. Medications that protect the heart and improve blood sugar control—such as SGLT2 inhibitors and GLP-1 receptor agonists—are often prescribed early. Lifestyle interventions, including dietary changes and exercise, become even more urgent.
The good news is that managing diabetes aggressively can slow or even partially reverse the progression of heart disease. Tight blood sugar control reduces inflammation, improves blood vessel function, and lowers the risk of future cardiac events. If you are diagnosed with both conditions, you are not facing two separate battles—you are treating one interconnected metabolic problem.
Practical steps to take
If you have heart disease and have not been screened for diabetes, ask your doctor for an A1c test. It is a simple blood draw and can provide life-changing information.
Even if your blood sugar is normal today, heart disease is a powerful reason to monitor it regularly over time. Lifestyle measures that help your heart—a balanced diet rich in vegetables, lean protein, and whole grains; regular physical activity; stress management; and adequate sleep—are the same measures that protect against diabetes.
Paying attention to your waist circumference is also useful. Excess abdominal fat is a strong marker of insulin resistance. If your pants size has been increasing even as you stay at the same weight, it is worth a conversation with your healthcare provider.
Takeaway message
Your heart and your blood sugar are not separate systems. They are deeply connected through metabolism, inflammation, and blood vessel health. For many people, a heart attack is not just a heart problem—it is the first visible sign that their body has been struggling with insulin resistance for years. Recognizing this can lead to earlier treatment, better outcomes, and a longer, healthier life.
If you or someone you care about has been diagnosed with heart disease, do not assume diabetes is not part of the picture. Ask for the test. The answer could change everything.
