The chemicals in tobacco smoke harm your heart and blood vessels in many ways. For example, they:
Thicken your blood and make it harder for your blood to carry oxygen.
Increase your blood pressure and heart rate, making your heart work harder than normal.
Lower your HDL cholesterol (sometimes called "good" cholesterol) and raise your LDL cholesterol (sometimes called "bad" cholesterol). Smoking also increases your triglyceride level. Triglycerides are a type of fat found in the blood.