One heartbeat is a repeating cycle of contraction (systole) and relaxation (diastole). Step through the phases and hear where the “lub-dub” comes from.
Atrial systole
The cardiac cycleone heartbeat
The phases
📷 Reference image
A real labeled figure to compare with the interactive above.
The Cardiac Cycle — OpenStax, CC BY 3.0 (via Wikimedia Commons)
