A 40-year-old woman applied for a preventive examination. Periodically notes the rare short stitching pains in the region of the heart. Weight 90 kg and height 170 cm, smokes 1 pack a day for 5 years, does not exercise. The last survey was 6 years ago. Mother suffered myocardial infarction at the age of 45 years. Physical examination revealed no pathology. What diagnostic examination should be carried out first?