This study examined the effect of the phenylalkylamine calcium channel blocker verapamil, on resting left ventricular (LV) function and O2 uptake rate (VO2) during exercise at maximal and submaximal work rates. Nine older hypertensive (71 years; OH), 10 older sedentary normotensive (69 years; OS), 10 older active (71 years; OA) and 10 young (24 years; Y) individuals volunteered. Studies were completed in the control condition and 4-6 h following 240 mg verapamil SR per os. Resting LV systolic (fractional shortening; FS) and diastolic (early : late (E/A) flow velocity ratio and isovolumic relaxation time (IVRT)) were measured by Doppler echocardiography. Maximal oxygen uptake (VO2,max) and, on subsequent test days, four transitions to and from a 6 min square wave exercise perturbation at a sub-anaerobic threshold intensity of 40 W (OH, OS, OA) or 100 W (Y) for determination of VO2 kinetics were performed on a cycle ergometer. Breath-by-breath VO2 transients were fitted with a monoexponential equation, starting at phase 2 of the response, while heart rate (HR) was fitted from phase 1, for the determination of the time constant of VO2 ([tau]VO2) and HR ([tau]HR). Baseline left ventricular FS was significantly greater in the OS (32 %), OA (34 %) and Y (34 %) than in the OH (23 %) groups, while E/A was significantly greater in the OA (1Σ16) and Y (2Σ34) than in the OH (0Σ9) and OS (0Σ82) groups (P < 0Σ05). Baseline VO2,max was higher and [tau]VO2 faster in the young (41Σ4 ml kg-1 min-1; 25Σ2 s) than in the older groups and in the OA (28Σ8 ml kg-1 min-1; 44Σ3 s) than in both OH (20Σ8 ml kg-1 min-1; 71Σ3 s) and OS (22Σ0 ml kg-1 min-1; 59Σ5 s) groups (P < 0Σ05). Heart rate kinetics showed similar differences to VO2 kinetics among the groups. After verapamil, no significant changes in FS, E/A or IVRT were observed in the OA and Y groups. In the OH group, FS (32 %) and E/A (1Σ15) increased while IVRT decreased significantly (from 0Σ103 to 0Σ07; P < 0Σ05). In the OS group, only E/A increased significantly (0Σ82 to 1Σ0; P < 0Σ05). None of the exercise variables (VO2,max, [tau]VO2 or [tau]HR) were altered for the OA or Y groups. VO2,max increased (from 20Σ8 to 22Σ8 ml kg-1 min-1) in the OH and (from 22Σ0 to 24Σ1 ml kg-1 min-1) in the OS (P < 0Σ05). [tau]VO2 was accelerated from 71Σ3 to 49Σ2 s in the OH group and from 59Σ5 to 48Σ2 s in the OS group (P < 0Σ05). These results suggest that VO2 responses at maximal and submaximal work rates may be dependent upon the initial cardiac pump function of the study population.