Cardiovascular training is very beneficial both to general health and to achieving your goal. Start running. Run however you want, but increase the pace, speed or both each time you run if you're trying to improve. Other ways to indirectly train the cardiovascular system include circuit training and many types of strongman exercises (farmers' walks, yolks, conan's wheels, sled drags, etc.). Doing olympic lifts for reps will also tire you out quickly.