Cardiac glycosides are much like any other glycoside, with an aglycone (nonsugar) and glycone (sugar) part, and act to slow and strengthen the heartbeat, digitalis (foxglove) glycosides are used as heart medications.
Others are found in lilly of the valley (convallaria), 'upas' tree (antiaris toxicofera IIRC, which is extremely toxic and rapidly acting) , Strophanthus species and oleanders amongst other plants, which are often used by natives of the indigenous area for arrow poisons.
Nothing that isn't going to show up on a GC/MS examination though.