The distinctive sound of a heartbeat - lub-dub, lub-dub, lub-dub - comes from two pairs of valves that are closing in the chambers of our heart. The valves are like turnstiles, allowing blood to move in one direction through heart and keep it from backing up.
Regardless of whether a red blood cell is heading to the lungs or is on its way to arteries and the rest of your body, the blood will have to pass through two different chambers and two different valves as it leaves the heart and goes onto its destination.
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