Cardiovascular diseases are increasingly becoming one of the leading diseases causing morbidity and mortality in Uganda. Ethnographic evidence suggests that these diseases are often first managed by indigenous and related herbs before patients are referred for allopathic forms of management. One such herb of interest is Nerium oleander. Therefore the crude ethanolic extracts of the dried leaves of this herb were tested against the following parameters in the isolated guinea pig hearts: force of contraction, heart rate and cardiac flow. The extracts brought about dose-dependent increases in all these parameters from their baseline readings. Compared with graded doses of digoxin the effects closely mirrored the activities in a dose dependent manner. At the mechanism of action level, it would appear the extract works in the same as digoxin since their dose-contraction-response curves are parallel. This finding would tend to provide a strong rationale for the herb's traditional use in cardiovascular illness.