Dipyridamole stress has the well known coronary vasodilator effects mediated by the inhibition of adenosine cellular transport, eventually leading to extra cellular adenosine accumulation and steal phenomena. There is a mild catecholamine release that is responsible for the inotropic effect of the drug: normal contractile reserve is present if the force-frequency relation is up sloping instead that abnormal negative. Lower panels. The ventricular force is expressed as SP/ESV assessed by echocardiography in the stress echo lab. Left, the mild increase in heart rate at peak stress is accompanied by a mild decrease in systolic pressure without decrease of the end-systolic volume. The Δ rest-peak SP/ESV index is <0 mmHg/ml/m2 (negative contractile reserve). Right, the mild increase in heart rate is accompanied by a mild decrease in systolic pressure with a more pronounced decrease of the end-systolic volume. The Δ rest-peak SP/ESV index is >0 mmHg/ml/m2 (normal contractile reserve). Upper panels. Sensor built force-frequency relation simultaneously recorded in the same patients in which standard echo force-frequency relation was built. Left, abnormal negative force-frequency relation: the Δ rest-peak force is less than 0.35 g * 10-3 (0.35 g * 10-3 = cut-off value for positive vs. negative contractile reserve in DIP stress). Right, normal contractile reserve: the Δ rest-peak force is >0.35 g * 10-3.