The effects of delta-9-tetrahydrocannabinol (cannabis) on cardiac performance with and without beta blockade.

Systolic time intervals (STI) were measured in ten healthy male volunteers before and after intravenous (i.v.) administration of 25 mug/kg delta-9-tetrahydrocannabinol (delta-9-THC). Mean +/- SEM heart rate increased 32 +/- 7 beats/min, while systolic and diastolic blood pressures were unchanged after delta-9-THC. Total electromechanical systole lengthened 17 +/- 4.2 msec, left ventricular ejection time (LVETc) prolonged 24 +/- 4.0 msec and pre-ejection period (PEP) shortened 17 +/- 5.1 msec after delta-9-THC. All of these changes were significant (P less than 0.01). In nine other subjects who underwent prior beta adrenergic blockade, similar but less marked changes were noted in heart rate, blood pressure, and STI after delta-9-THC. The shortening of PEP after delta-9-THC was only 9 msec (NS) in beta blocked subjects. Thus, delta-9-THC significantly increased heart rate, shortened PEP and prolonged LVETc without any change in afterload. Beta adrenergic blockade prevented significant shortening of PEP and blunted other responses. These findings suggest that delta-9-THC enhanced cardiac performance. Partial inhibition of this effect was achieved with prior beta adrenergic blockade.