High-intensity interval training (HIIT) benefits cardiovascular fitness by improving heart rate, enhancing oxygen uptake, and increasing aerobic capacity. The alternating periods of intense exercise and rest can lead to improved metabolic function, greater calorie burn, and overall endurance. Research shows that HIIT can lead to similar or even superior improvements in cardiovascular health compared to traditional endurance training, making it an efficient workout option for those looking to enhance their fitness levels in a shorter timeframe.