Smoking adversely affects cardiovascular fitness by damaging blood vessels and reducing oxygen supply to the heart. It leads to increased heart rate, elevated blood pressure, and decreased exercise capacity, making physical activities more demanding. Long-term smoking contributes to atherosclerosis, where arteries become narrowed, hindering blood circulation. This can lead to severe complications such as heart attacks and strokes. Quitting smoking significantly improves cardiovascular health over time and enhances fitness levels by improving lung capacity and overall stamina.