Only the first of the four images is cited in copyright info but here are all four citations.  

1. Laboratoires Servier, Cardiovascular system - The cardiac cycle 1 -- Smart-Servier.png. CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons. Oct 2016. https://upload.wikimedia.org/wikipedia/commons/7/79/Cardiovascular_system_-_The_cardiac_cycle_1_--_Smart-Servier.png

2. Laboratoires Servier, Cardiovascular system - The cardiac cycle 2 -- Smart-Servier.png. CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons. Oct. 2016 https://upload.wikimedia.org/wikipedia/commons/1/13/Cardiovascular_system_-_The_cardiac_cycle_2_--_Smart-Servier.png

3. Laboratoires Servier, Cardiovascular system - The cardiac cycle 3 -- Smart-Servier.png CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons. Oct 2016. https://upload.wikimedia.org/wikipedia/commons/7/7f/Cardiovascular_system_-_The_cardiac_cycle_3_--_Smart-Servier.png

4. Laboratoires Servier, Cardiovascular system - The cardiac cycle 4 -- Smart-Servier.png CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons. Oct 2016 https://upload.wikimedia.org/wikipedia/commons/c/c9/Cardiovascular_system_-_The_cardiac_cycle_4_--_Smart-Servier.png