Diastolic and systolic time intervals were measured in 11 control subjects, 11 patients with cardiomyopathy, 7 hyperthyroid patients, and 5 hypothyroid patients. The isovolumic relaxation time (IVRT), rapid filling time (RFT), preejection period (PEP), left ventricular ejection time (LVET), and PEP/LVET ratio were found by simultaneously recording the ECG, phonocardiogram, external carotid pulse, and apexcardiogram. In cardiomyopathy the IVRT and RFT were prolonged (107.4 +/- 21.1 msec [P less than 0.01] and 111.0 +/- 10.0 [P less than 0.01] respectively) in comparison to the control subjects. (In the controls the IVRT was 85.7 +/- 18.4 msec and the RFT was 94.5 +/- 12.8 msec). In altered thyroid states the RFT was most affected; in hypothyroidism it increased to 123.9 +/- 25.2 (P less than 0.01) and in hyperthyroidism it decreased to 71.5 +/- 21.3 msec (P less than 0.01). In hyperthyroid patients the IVRT, although shorter than in control subjects, was not significantly altered, but it showed a significant increase after treatment. The RFT also returned toward normal after therapy in both groups (116.7 +/- 14.6 msec in hypothyroid patients and 89.0 +/- 23.1 msec in those with hyperthyroidism).