The sound of a heartbeat is caused by
- The lub dub sound of a heartbeat is caused by
- The lub sound of the heartbeat is caused by
- The sound of the heartbeat is primarily caused by
- The sound of the heartbeat lub-dub is caused by
- The lub dub sound of your heartbeat is caused by
- The first sound of the heartbeat is caused by the ___ valves closing
- The second sound of the heartbeat is caused by the ___ valves closing
- The sound of the heartbeat heard through a stethoscope is caused by
- The sound of a heartbeat