Heart‐rate and ECG (including 5 precordial leads) responses were studied in 16 healthy subjects during up to 6 min exposure to 3‐3 1/2 times the force of gravity in a human centrifuge. The subjective g tolerance (resistance to dimming or loss of vision) was determined in relation to various circulatory functional and dimensional parameters. The ECG did not show any remarkable alterations during or after the runs. Subjective g tolerance was correlated to orthostatic heart‐rate (produced by normal gravity) but not to heart‐rate response under increased gravitational stress, physical working capacity, heart volume in the horizontal or vertical body position, or total hemoglobin.