The exercise that improves cardiovascular endurance the most is running. Running, particularly at a steady pace over long distances, effectively enhances the heart and lung capacity. It increases VO2 max, which measures the body’s ability to consume and utilize oxygen during intense exercise. Other effective activities include cycling and swimming, but running tends to provide the greatest cardiovascular benefits due to its accessibility and ability to be adjusted to various fitness levels. Regular running sessions significantly strengthen cardiovascular health and overall endurance.