Antagonistic effects of excitation and interval on tension in guinea pig atria.
D000818:Animals; D005117:Cardiac Complexes, Premature / Q000503:physiopathology*; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D006325:Heart Atria; D006339:Heart Rate; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009206:Myocardium; D013997:Time Factors