To determine if an isolated right ventricular wall infarct (RVI) alters right ventricular diastolic function (RVDF), 6 mongrel dogs were studied before and after a right ventricular wall infarct was produced by ligating the right coronary artery and embolizing the distal right coronary artery with mercury. Right ventricular diastolic function was assessed by prior instrumentation of the animals with an RV Millar catheter and segment length crystals attached to the infarct (I) and non-infarct (NI) territory of the right ventricle. The time constant of RV isovolumic relaxation (Tau) was assessed by fitting right ventricular pressure decline after minimum dp/dt to the equation 1nP = At + B, where A represents the slope of the relationship, a negative number, tau = -1/A. The right ventricular diastolic pressure segment length relationship (RVD PSR) was analyzed using a multiple linear regression model whereby the independent effects of heart rate, segment length, and right ventricular wall infarct could be assessed. Right ventricular wall infarct reduced stroke volume to 63% of baseline values largely by increases in RV-I end-systolic segment length. Tau was significantly prolonged. However, there was no significant upward shift in RVDPSR in any animal. These data suggest that in this model RV diastolic relaxation is impaired. However, the degree of this impairment is not significant enough to shift the right ventricular diastolic pressure segment length relationship, as long as the pericardium remains open.