In different cell types, activation of signal transduction pathways leads to the generation of calcium oscillations and/or waves. Due to this important impact for cellular function, calcium waves are the subject of intensive investigations. To study interactions of cell organelles with no influence of the cell membrane, sarcoplasmic reticulum (SR) vesicles and well-coupled mitochondria were reconstituted. For the first time, we demonstrate the generation and propagation of calcium waves in a suspension of sarcoplasmic reticulum vesicles, embedded in an agarose gel. The propagation dynamics resemble those of calcium waves in living cells. Moreover, the addition of well-coupled mitochondria leads to more pronounced and significantly faster propagating waves, demonstrating the importance of the mitochondrial Ca(2+) transport. The experimental and simulation results indicate the resemblance of the in vitro system to an excitable medium.