Patients with systemic sclerosis (SS) have cardiac dysfunction induced by cold exposure. We and others have demonstrated this finding after corporal chilling, suggesting a "coronary Raynaud phenomenon" mediated by intermittent vascular spasm. In this study we evaluated the effect of diltiazem (DTZ) in cardiac dysfunction induced by cold test in patients with SS without clinical evidence of heart disease. Twelve patients with SS were studied. One patient was excluded because he did not fulfill the prescribed treatment. Eleven patients (age of 49.9 +/- 3.8 years and illness duration of 9.3 +/- 4.8 years) were included. Gated equilibrium radionuclide ventriculography was recorded after red blood cells were labeled in vivo using an intravenous injection of stannous pirophosphate followed by 20 mc of 99 Tc (gamma camera with electrocardiographic R wave gating was used). Left ventricular injection fraction (LVEF) was calculated using computer analysis and wall motion abnormalities by visual interpretation. Patients were cooled using a thermic blanket set at 5 degrees centigrade. They were evaluated before and after a period of cooling. After corporal chilling LVEF decreased more than 10% in all of them. DTZ 270 mg a day was administered to the same patients during 48 hs. Basal and cold LVEF were repeated in all patients. The results with and without DTZ were compared by Student's t Test. The basal LVEF with and without DTZ was not different (64.8 +/- 2.6 and 63.1 +/- 1.8). After corporal chilling LVEF decreased (64.8 +/- 2.6 to 54.8 +/- 2.5 p < 0.00001) and reversible abnormalities in wall motion were noticed in patients without DTZ. When they received DTZ neither difference in LVEF (63.1 +/- 1.8 to 62.1 +/- 2.4) nor wall motion abnormalities were observed. We compared the LVEF after chilling (62.1 +/- 2.4 and 54.8 +/- 2.5) and we found an important difference with the use of DTZ (p < 0.005). It can be concluded that in patients with SS and no overt heart disease, DTZ prevents the early cardiac dysfunction induced by cold test. Probably this drug blunts the coronary spasm induced by cold test in this group of patients.