(1) Background: This study aimed to analyze epidemiological data to identify risk factors for silent myocardial ischemia in patients with long-term type 1 and type 2 diabetes. (2) Methods: An analysis was performed on 104 patients with long-term type 1 and type 2 diabetes who had not previously been diagnosed with cardiovascular disease. During hospitalization, patients were subjected to a standard ECG exercise test on a treadmill. If the test could not be performed or the result was uncertain, a pharmacological exercise test with dobutamine was performed. In the case of a positive exercise ECG test or a positive dobutamine test, the patient underwent coronary angiography. (3) Results: Atherosclerotic lesions were found in 24 patients. Patients with silent ischemia were significantly older and had a lower mean left ventricular ejection fraction and a higher incidence of carotid atherosclerosis. The presence of microvascular complications did not increase the risk of silent ischemia. (4) Conclusions: Silent heart ischemia is more common in type 2 than type 1 diabetes. Predisposing factors include older age, coexistence of carotid atherosclerosis, lower left ventricular ejection fraction, and smoking in patients with type 1 diabetes. Concomitant microvascular complications are not a risk factor.