You start the chronograph hand and count the required number of beats - most watches are adjusted to 15 or 30. Once you reach the required number you stop the chrono, the number on the bezel will correspond to your heartbeat.
Verdict: Angine. Before that the doctor came, and to my surprise he measured her heart beat using a watch and a pulsometer scale. Made me think that these things were actually used as intended. Now I kinda want a chronograph...